Control device for a PWM controlled converter having a voltage controller

ABSTRACT

A control device for a PWM controlled converter having a voltage control portion for comparing with a voltage set value a detected value of a DC voltage output from the PWM controlled converter, connected through reactors to a 3-phase AC power source, for controlling AC input currents supplied from the 3-phase AC power source, to thereby produce current reference signals; an AC reference signal generating portion for generating AC reference signals synchronized with the 3-phase AC power source; a current instruction portion for producing current instruction signals formed by varying the amplitudes of the AC reference signals output from the AC reference signal generating portion in accordance with the current reference signals, and a current control portion for producing control signals to the PWM controlled converter so that the AC input currents vary as instructed by the current instruction signals. The control device portion produces control signals based on a proportional control for a predetermined period after the control starts, and produces other control signals based on a proportional integration control after the predetermined period is terminated.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control device for a PWM controlledconverter which converts an AC power source voltage into a DC voltage.

2. Description of the Related Art

There are many devices which convert AC power to DC and the number ofsuch devices is increasing. In this type of device, an AC power sourcevoltage is converted into a DC voltage, and the converted DC voltage isused. In the AC to DC converting operation, reactive power and harmonicsare generated, which causes some problems. To solve these problems, aPWM controlled converter has been proposed as a device for converting anAC power source voltage into a DC voltage.

FIG. 28 is a block diagram showing a conventional control device for aPWM controlled converter. The control device for a PWM controlledconverter is as discussed in "Method for Controlling a P-phase Invertornot Using an Insulating Transformer", 1991 National Convention RecordIEEE Japan, pp 5 to 80, or as disclosed in Japanese Patent Laid-OpenPublication No. Hei. 3-212162.

In the figure, reference numeral 1 designates a 3-phase AC power source;numeral 2, a PWM controlled converter which converts AC power receivedfrom the 3-phase AC power source 1 into a DC voltage-by controlling theAC current of the received AC power, and outputs the converted DCvoltage; numerals 201 to 206 designate switching elements which aretransistors, IGBTs (insulated gate bipolar transistors) and the like;and 207 to 212 designate circulating diodes. Numeral 3 designatesreactors connected between the 3-phase AC power source 1 and the PWMcontrolled converter 2; 4 designates a smoothing condenser for absorbinga pulsating component contained in an output current of the PWMcontrolled converter 2; 5 designates a load unit, such as an invertor ora resistive component; 6 designates a voltage setter for outputting avoltage setting signal for setting a DC voltage output from the PWMcontrolled converter 2; and 7b designates a voltage detecting circuitfor detecting a DC voltage output from the PWM controlled converter 2.

Numeral 8 indicates a subtractor for calculating a deviation of avoltage detecting signal detected by and output from the voltagedetecting circuit 7b from a voltage setting signal set by and outputfrom the voltage setter 6; 9d designates a voltage controller whichincludes a proportional control calculating element and a proportionalintegration calculating element, and proportional integration (PI)controls a deviation of a voltage detecting signal output from thesubtractor 8 from the voltage setting signal; 10 designates an ACvoltage detector for detecting an AC voltage from the 3-phase AC powersource 1; 11 designates a unit sine wave generator for generatingR-phase and T-phase unit sine waves, which are synchronized with R-phaseand T-phase voltages, from an AC voltage detecting signal detected bythe AC voltage detector 10; 12 and 13 designate multipliers formultiplying a peak value instruction signal of an input current receivedfrom the voltage controller 9d by R-phase and T-phase unit sine wavesignals received from the unit sine wave generator 11, and outputsR-phase and T-phase input current instruction signals.

Numerals 14 and 15 represent current detectors for detecting currents ofR-phase and T-phase input to the PWM controlled converter 2; 16 and 17represent subtractors for producing a deviation of an input currentdetecting signal of R-phase output from the current detector 14 from aninput current instruction signal of R-phase output from the multiplier12 and a deviation of an input current detecting signal of T-phaseoutput from the current detector 15 from an input current instructionsignal of T-phase output from the multiplier 13; 18b and 19b representR- and T-phase current controllers which include proportional controlcalculating elements and proportional integration calculating elements,and proportional integration (PI) control the deviations of the T-phaseinput current detecting signals from the R-phase input currentinstruction signals, to thereby output an R-phase control signal and aT-phase control signal; 20 represents a subtractor for subtracting fromzero the R- and T-phase control signals output from the R- and T-phasecurrent controllers 18b and 19b; 21 represents a carrier waveoscillator; 22, 23 and 24 represent comparators for comparing theamplitudes of R-, S- and T-phase control signals with a carrier wavesignal to output pulse-width modulated signals; 25 represents a gatecircuit for outputting signals to turn on and off the switching elements201 to 206 of the PWM controlled converter 2 in accordance with R-, S-and T-phase pulse-width modulated signals.

An operation of the conventional control device thus constructed will bedescribed. A detecting value V DC of a DC voltage detected by thevoltage detecting circuit 7b and a detecting value V DC* set by thevoltage setter 6 are input to the subtractor 8 where the eV(deviation)=V DC -V DC* is calculated. The obtained deviation eV isinput to the voltage controller 9d where it is PI-controlled to producea peak value instruction signal I PEAK* of the input current. The peakvalue instruction signal I PEAK is applied to the multipliers 12 and 13where it is multiplied by the unit sine wave signals of R-phase andT-phase which are other signals input to the multipliers. The R- andT-phase unit sine wave signals are reference AC signals synchronizedwith the R- and T-phase voltages of the 3-phase AC power source 1, andare generated by a current reference signal generator constituting theunit sine wave generator 11, which receives an AC voltage of the 3-phaseAC power source 1 detected by the AC voltage detector 10. Themultipliers 12 and 13 produce an R-phase input current instructionsignal iR* and a T-phase input current instruction signal iT*,respectively.

The R-phase input current instruction signal iR*, which is an outputsignal of the multiplier 12, and an R-phase input current detectingsignal iR, which is an output signal of the current detector 14, areapplied to the subtractor 16 which calculates eiR (deviation)=iR*-iR andoutputs the result of the calculation. Similarly, the T-phase inputcurrent instruction signal iT*, which is an output signal of themultiplier 13, and a T-phase input current detecting signal iT, which isan output signal of the current detector 15, are applied to thesubtractor 17 which calculates eiT (deviation)=iT*-iT and outputs theresult of the calculation. The current deviations eiR and eiT areapplied to the R-phase current controller 18b and the T-phase currentcontroller 19b, respectively. These current controllers PI-control thecurrent deviations and output S- and T-phase control signals SR* andST*, respectively.

An S-phase control signal SS* is produced in a manner that thesubtractor 20 subtracts the R- and T-phase control signals SR* and ST*from zero. The R-, S- and T-phase control signals SR*, SS* and ST* asthe output signals of the R-, S- and T-phase current controllers 18b, 20and 19b, are applied to the comparators 22, 23 and 24, respectively.Those comparators compare the amplitudes of the control signals SR*, SS*and ST* with the amplitude of a triangle wave carrier signal, andproduce pulse width modulation (PWM) signals. The PWM signals areapplied to the gate circuit 25. The gate circuit outputs control signalsso that a detecting value V DC of a DC voltage of the PWM controlledconverter 2 is equal to a detecting value V DC*, and so that the R-, S-and T-phase input currents iR, iS and iT are equal to the R-, S- andT-phase input current instruction signals iR*, iS* and iT* as sine wavesignals. In the PWM controlled converter 2, the switching elements 201to 206 are turned on and off in accordance with the control signalsreceived from the gate circuit.

In the thus constructed control device for a PWM control converter, asdescribed above, the R- and T-phase current controllers 18b and 19b forma current control loop in which the R- and T-phase input currentinstruction signals iR* and iT* output from the multipliers 12 and 13are used as instruction signals, and the R- and T-phase input currentdetecting signals iR and iT output from the current detectors 14 and 15are used as feedback signals. The R- and T-phase current controllers 18band 19b may be realized by a digital control technique using amicroprocessor, for example, or an analog control technique usingoperation amplifiers, for example. When the digital control technique isused, sampling delays entail time lags. Therefore, in designing thecurrent controllers, it is impossible to increase a response in thecontrol system of the digital control basis current controller in excessof that of the analog control basis current controller. Therefore, inthe digital control basis current controller, the followingdisadvantageous phenomena inevitably take place: on and off delays ofthe switching elements 201 to 206 in the PWM controlled converter 2, adeviation of an actual voltage that is caused by an on voltage from thevoltage instruction value V DC*, a waveform distortion of an AC inputvoltage of the 3-phase AC power source 1, and the like. Accordingly, anAC input current waveform is not sinusoidal and contains harmonicsdefined by the waveform distortion.

To make the input current waveform faithfully trace a sinusoidalwaveform, the analog control system that has no sampling delays, forexample, and enables the current control system to have a high responseis preferably used for the current controllers. Similarly, to make a DCvoltage value in the PWM controlled converter 2 follow the set value, itis preferable to construct the voltage controller 9d on the basis of theanalog control system which is free from the sampling delays, forexample, and allows the voltage control system to have a high response.

FIG. 29 is a circuit diagram showing in detail the R- or T-phase currentcontroller. In the circuit diagram, the R-phase current controller 18bas an IP controller which performs an analog control of current, and isrealized by using an operational amplifier.

In FIG. 29, reference numerals 101 to 103 designate fixed resistors;numeral 104, a capacitor; 105, an operational amplifier; 106 and 107,positive and negative voltage input terminals of a control power sourcefor driving the operational amplifier 105; 108, an input terminal; and109, an output terminal. In the thus constructed R-phase currentcontroller 18b, when an input signal at the input terminal 108 that ispositive or negative continues for a fixed period of time or longer, thevoltage across the capacitor 104, which provides an integration term ofa proportional integration operation, increases in the positive ornegative direction. However, it is possible for the capacitor voltage toincrease to be below a positive voltage or above a negative voltage ofthe control power source applied through the positive and negativevoltage input terminals 106 and 107. Thus, the capacitor voltage issaturated while being limited within a fixed value. Also, when an inputsignal coming in through the input terminal 108 is large, a signaloutputted from the operational amplifier 105 after a signal amplifyingprocess by the amplifier cannot vary to be below a positive voltage orabove a negative voltage of the control power source applied through thepositive and negative voltage input terminals 106 and 107. The outputsignal of the operational amplifier is saturated within a limited value.

The T-phase current controller 19b is also similarly constructed andoperates in a similar manner. The circuit constructed as stated above isa basic circuit, generally used for realizing a proportional integrationoperation by using an operational amplifier.

FIG. 30 is a circuit diagram showing a specific example of the voltagedetecting circuit 7b for detecting a DC voltage V DC. In FIG. 30,reference numeral 701 designates an input terminal connected to apositive potential of the smoothing condenser 4; and 702 and 703designate fixed resistors for dividing a DC voltage V DC. The fixedresistor 703 is connected to a negative potential of the smoothingcondenser 4. Numeral 704 designates an insulated amplifier; 705 and 706,fixed resistors; 707, an operational amplifier; and 708 and 709designate variable resistors for adjusting an offset and a gain of thevoltage detecting value. The thus constructed circuit is a basiccircuit, which is generally used for adjusting offset and gain errors byan operational amplifier, and includes variable resistors for adjustingthe offset and the gain errors.

In the conventional control device for a PWM controlled converter thusconstructed, an overcurrent problem arises particularly when the controldevice is started up in a state that electric power has been suppliedfrom the 3-phase AC power source 1 to the load unit 5.

In a case where electric power has been supplied from the 3-phase ACpower source 1 to the load unit 5 in a state that the switching elements201 to 203 of the PWM controlled converter 2 are in an off state, viz.,before the control by the PWM controlled converter 2 starts and the gatecircuit 25 is closed, the power is supplied to the load unit 5, throughthe reactors 3 and the circulating diodes 207 to 212. In this case, thewaveforms of the R-, S- and T-phase input currents are as shown in FIG.31.

In this case, the current flows through the reactors 3. Because of this,an input voltage of each phase to the PWM controlled converter 2 islower than the voltage of the 3-phase AC power source 1 by a voltagecorresponding to a voltage drop across the corresponding reactor 3. As aresult, a DC voltage, or a voltage across the smoothing condenser 4, ofthe PWM controlled converter 2 is lowered.

When the controlling operation of the control device is started up fromthis state, the R- and T-phase current controllers 18b and 19b operateso as to compensate for a lowering of the DC voltage V DC. The R-and-T-phase control signals SR* and ST* output from those currentcontrollers 18b and 19b increases substantially inversely proportionalto the DC voltage V DC. In the conventional control device for a PWMcontrolled converter, the R- and T-control signals SR* and ST* areobtained through the calculations of the R- and T-phase currentcontrollers 18b and 19b which perform PI operations, and the S-phasecontrol signal SS* is obtained as SS*=(-SR*-ST*), which follows from aformula SR*+SS*+ST*=0. Since the current controllers operate so as tocompensate for a lowering of the voltage V DC, when the R- and T-phasecontrol signals SR* and ST* increase in the positive or negativedirection and are saturated and fixed at a predetermined value, theS-phase control signal SS* is also fixed at a predetermined value. As aresult, the control device fails to control the voltages of the threephases. Particularly, at the time of the above-mentioned starting upwhere the currents as shown in FIG. 31 flow, the current deviations asthe input signals to the R- and T-phase current controllers 18b and 19bare connected to a positive or negative polarity for a fixed period oftime. Therefore, a value of the integration term as a constituentelement increases, so that the output signals of the R- and T-phasecurrent controllers 18b and 19b are frequently saturated. As a result,the control device fails to control the voltages of three phases, anovercurrent flows in the control device and possibly drives anovercurrent protecting mechanism to trip. Incidentally, the overcurrentprotecting mechanism is generally incorporated into the circuit forprotecting circuit elements.

Also in a normal running state, when an electric power of the load unit5 abruptly changes and the voltage V DC drops, the output signals of theR- and T-phase current controllers 18b and 19b are saturated as at thetime of the above-mentioned starting up. The control device fails tocontrol the voltages of three phases including the S-phase, anovercurrent flows in the control device, and possibly causes a trip ofthe protecting mechanism.

Also in a case where the voltage V DC is controlled as indicated by aset value, when the R- and T-current deviations eiR and eiT as the inputsignals to the R- and T-phase current controllers 18b and 19b becomelarge as the result of an abrupt change of the current instructionsignal, the proportional terms as the constituent elements of the R- andT-phase current controllers 18b and 19b become large, the output signalsof the R- and T-phase current controllers 18b and 19b are saturated, andconsequently the control device fails to control the voltages of threephases including the S-phase, an overcurrent flows in the controldevice, and possibly causes a trip of the mechanism.

In the control device for a PWM controlled converter, the analog controltechnique using the operational amplifier is widely used forconstructing the voltage controller 9d since it is necessary toprecisely control the DC voltage that appears at the output of the PWMcontrolled converter 2. The voltage controller 9d receives a deviationeV of a detecting value V DC detected by the voltage detecting circuit7b from a set value V DC* set by the voltage setter 6; eV=V DC*-V DC .Then, it PI controls the deviation eV to produce a peak valueinstruction signal I PEAK* of the input current. Therefore, the voltagedetecting circuit 7b must contain a means for correcting and adjustingan offset error and a gain error of the voltage detecting circuit perse. To this end, variable resistors are used. It is difficult toautomate the adjustment by the variable resistors. Therefore, intricateand troublesome work is essential at the time of manufacturing andadjusting.

Since the control device for a PWM controlled converter is thusconstructed, particularly when the voltage of the 3-phase AC powersource 1 drops or is interrupted for a short time by, for example, aninstantaneous power interruption, an overcurrent problem arises when thepower voltage is returned to the original one.

The problem stated above will be described hereunder.

FIG. 32 shows waveforms of an R-phase power source voltage eR, anR-phase input current instruction signal iR*, and an R-phase inputcurrent detecting signal iR. Those waveforms are correspondingly appliedto the waveforms of S- and T-phase. Only the waveforms of those signalsand voltage of R-phase will be typically described. The followingrelation holds among the R-phase power source voltage eR, the R-phaseinput voltage vR of the PWM controlled converter 2, and the R-phaseinput current detecting signal iR:

    eR=L (diR/dt)×VR

In the above expression, L indicates an inductance value of the reactor3. The resistance value of the reactor 3 is negligible. Therefore, it isleft out of consideration here. In a general PWM controlled converter,the voltage drop across the reactors 3 is several to several tens % ofthe power source voltage eR. Accordingly, the power source voltage eRand the input voltage vR of the PWM controlled converter 2 aresubstantially in phase.

In a normal operating condition, the R-phase current controller 18boperates so that the R-phase input current detecting signal iR followsthe R-phase input current instruction signal iR*, and produces anR-phase control signal SR*. The R-phase current controller 18b PIcontrols a deviation of the R-phase input current detecting signal iRfrom the R-phase input current instruction signal iR*. A proportionalgain and an integration gain are set at negative values so as todecrease the R-phase control signal SR* when the R-phase input currentinstruction signal iR* is larger than the R-phase input currentdetecting signal iR, viz., the current is increased in the positivedirection. The amplitude of the R-phase control signal SR is comparedwith that of a triangle wave carrier signal output from the carrier waveoscillator 21, and the result of the comparison is output in the form ofa pulse width modulation signal. The pulse width modulation signalreflects on the R-phase input voltage vR to PWM controlled converter 2.

When the 3-phase AC power source 1 is interrupted by, for example, aninstantaneous power interruption, no input current flows. As a result, adifference is caused between the R-phase input current instructionsignal iR and the R-phase input current detecting signal iR. An R-phasecontrol signal SR*, which is opposite in direction to the R-phase inputcurrent instruction signal iR*, is caused as shown in FIG. 33. Usually,the R-phase input current instruction signal iR* is controlled to besubstantially in phase with the R-phase power source voltage eR. When aninstantaneous power interruption takes place, a voltage opposite inpolarity to the R-phase power source voltage eR is output as the R-phaseinput voltage vR of the PWM controlled converter 2. Particularly, whenthe R-phase current controller 18b is designed using the analog controltechnique to have a high response in its control system, theaccumulation of a value of the integrating element of the R-phasecurrent controller 18b increases in the opposite polarity for a shorttime.

The phase of the output signal of the unit sine wave generator 11 isused as the reference phase of the R-phase input current instructionsignal iR*. Usually, the unit sine wave generator 11 is constructed witha circuit having a fixed time constant, and the like. Therefore, even ifthe 3-phase AC power source 1 is interrupted for a short time, the phaseof the power source voltage remains invariable.

When the power source voltage is returned to its original voltage, orthe power source is restored from its interruption, a difference betweenthe R-phase power source voltage eR and the R-phase input voltage vR tothe PWM controlled converter 2 is large. The large difference of voltageis applied across the reactor 3, so that the R-phase input currentdetecting signal iR abruptly-increases. The abruptly increased current(referred to as a spike current) possibly causes an overcurrentprotecting mechanism to trip. Incidentally, the overcurrent protectingmechanism is generally incorporated into the circuit for protecting theswitching elements 201 to 206.

When the input current instruction signal is large, for example, whenlarge power is supplied to the load unit 5, the R- and T-phase currentdeviations eiR and eiT as the input signals to the R- and T-phasecurrent controllers 18b and 19b are large, and a value of theintegration term as one of the component elements of each currentcontroller becomes larger. And a difference between the voltage and thepower source voltage of the related phase further grows. Consequently,the spike current caused at the time of the restoring of the powersource further increases, which in turn drives the overcurrentprotecting mechanism to trip.

The overcurrent problem description, which has been made about theR-phase AC input current control in the converter control device, iscorrespondingly applied to the same problem in the AC input currentcontrol of the other phases.

When the 3-phase AC power source 1 is interrupted for a long time, it iseasy to detect such an interruption. When the supply of the power sourceis interrupted for a short time as when an instantaneous power failuretakes place, particularly when the power interruption duration isapproximately 1/2 as large as the period of the power source frequencyor the power source voltage drop continues for such a short period, itis difficult to detect the power interruption. The conventional devicecannot reduce or suppress the spike current, the overcurrent or the likecaused when the power source recovers from a state that the voltage ofthe 3-phase AC power source 1 drops or the supply of the same isinterrupted for a short time because of an instantaneous power failure,for example.

The present invention has been made to solve the above problems of theconventional art, and an object of the present invention is to provide acontrol device for a PWM controlled converter which can satisfactorilycontrol an input current to the PWM controlled converter in a state thatwhen the control device is started up or the power of the load unitabruptly changes, the DC voltage at the output side of the PWMcontrolled converter drops or a deviation of the actual input currentfrom the input current instruction value as when the input currentinstruction value abruptly changes.

Another object of the present invention is to provide a control devicefor a PWM controlled converter which does not need variable resistorsfor compensating for the offset error and the gain error of the voltagedetecting circuits, improves the operability at the time ofmanufacturing and adjusting, and can easily automate the adjustingoperation of the offset and gain errors.

Yet another object of the present invention is to provide a controldevice for a PWM controlled converter which can satisfactorily controlan input current to the PWM controlled converter without causing anyspike current when an instantaneous power interruption, for example,takes place, the voltage of the power source drops or the supply of thepower source is interrupted for a short time, and the power source isrestored to its original state.

Still another object of the present invention is to provide a controldevice for a PWM controlled converter which can satisfactorily controlan input current to the PWM controlled converter without causing anyspike current also when the overcurrent protecting mechanism is easilytripped, for example, when the input current instruction value is large,the voltage of the power source drops or the supply of the power sourceis interrupted for a short time, and the power source is restored to itsoriginal state.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided acontrol device for a PWM controlled converter having voltage controlmeans for comparing with a voltage set value a detecting value of a DCvoltage output from the PWM controlled converter, connected throughreactors to a 3-phase AC power source, for controlling AC input currentssupplied from the 3-phase AC power source, to thereby produce currentreference signals, AC reference signal generating means for generatingAC reference signals synchronized with the 3-phase AC power source,current instruction means for producing current instruction signalsformed by varying the amplitudes of the AC reference signals output fromthe AC reference signal generating means in accordance with the currentreference signals, and current control means for producing controlsignals to the PWM controlled converter so that the AC input currentsvary as instructed by the current instruction signals, the improvementcharacterized in that the current control means produces control signalsbased on a proportional control for a predetermined period after thecontrol starts, and produces other control signals based on aproportional integration control after the predetermined period isterminated.

In the control device, the current control means produces the controlsignals based on the proportional integration control at the instantthat a detecting value of the DC voltage output from the PWM controlledconverter exceeds a predetermined value.

According to another aspect of the invention, there is provided acontrol device for a PWM controlled converter having voltage controlmeans for comparing with a voltage set value a detecting value of a DCvoltage output from the PWM controlled converter, connected throughreactors to a 3-phase AC power source, for controlling AC input currentssupplied from the 3-phase AC power source, to thereby produce currentreference signals, AC reference signal generating means for generatingAC reference signals synchronized with the 3-phase AC power source,current instruction means for producing current instruction signalsformed by varying the amplitudes of the AC reference signals output fromthe AC reference signal generating means in accordance with the currentreference signals, and current control means for producing controlsignals to the PWM controlled converter so that the AC input currentsvary as instructed by the current instruction signals, the improvementcharacterized in that the current control means multiplies thedeviations of AC input currents from the current instruction signals oftwo of three phases output from the current instruction means by firstcoefficients, integrates the results of the multiplications, and outputsthe results of the integrations in the form of first output signals ofthe two phases, adds together the sign inverse values of the firstoutput signals of the two phases to form a first output signal of theremaining phase, multiplies the deviations of the AC input currents fromthe input current instruction signals by second coefficients to formsecond output signals of the respective phases, adds together the firstand second output signals for each phase and outputs the sums in theform of control signals applied to the PWM controlled converter.

According to still another aspect of the invention, there is provided acontrol device for a PWM controlled converter having DC voltagedetecting means for detecting a DC voltage output from the PWMcontrolled converter for controlling AC input currents supplied from a3-phase AC power source, voltage instruction outputting means foroutputting an instruction value of the DC voltage, voltage control meansfor comparing a voltage instruction value output from the voltageinstruction outputting means with a voltage detecting value output fromthe DC voltage detecting means, to thereby produce current referencesignals, and current control means for producing control signals to thePWM controlled converter so that the AC input currents vary asinstructed by the current instruction signals obtained from the currentreference signals, the improvement characterized in that the voltageinstruction outputting means calculatingly corrects the detection errorsto produce a voltage instruction value.

In the control device, the voltage instruction outputting means includesstoring means for storing the relationships between the values of theknown voltages applied to the DC voltage detecting means and thedetecting voltage values, detected by the DC voltage detecting means,corresponding to the known voltages, and correcting means forcalculatingly correcting a voltage instruction value by using the storedvoltage relationships so that an actual DC voltage output from the PWMcontrolled converter is settled down at a desired value.

In the control device, the known voltages applied to the DC voltagedetecting means are DC voltages output from the PWM controlledconverter.

Also in the control device, the voltage instruction outputting meansincludes storing means for storing the relationships between thevoltages output from a reference voltage generating means included inthe DC voltage detecting means and the detecting voltage values,detected by the DC voltage detecting means, corresponding to thevoltages output from the reference voltage generating means, andcorrecting means for calculatingly correcting a voltage instructionvalue by using the stored voltage relationships so that an actual DCvoltage output from the PWM controlled converter is settled down at adesired value.

According to yet another aspect of the invention, there is provided acontrol device for a PWM controlled converter having voltage controlmeans for comparing a voltage set value with a detecting value of a DCvoltage output-from the PWM controlled converter, connected to an ACpower source, for controlling AC input currents supplied form the ACpower source, to thereby produce a current reference signal, ACreference signal outputting means for outputting AC reference signalssynchronized with the AC power source, current instruction means forproducing current instruction signals formed by varying the amplitudesof the AC reference signals output from the AC reference signaloutputting means in accordance with the current reference signal, andcurrent control means, including at least integrating elements, forproducing control signals to the PWM controlled converter so that the ACinput currents vary as instructed by the current instruction signals,the improvement characterized in that when an AC input current exceeds apredetermined limit value, the current control means abruptly reducesthe integrating elements thereof.

In the control device, when an AC input current exceeds a predeterminedlimit value, the current control means resets the integrating elementsthereof to zero (0).

Also in the control device, the limit value is set on the basis of thecurrent reference signal output from the voltage control means.

In the control device, the limit value is set on the basis of thecurrent instruction signals output from the current instruction means.

The current control means includes a current limit level-setter forsetting a limit value of an AC input current and a current controllerintegration reset circuit connected for reception to the limit value setby the current limit level setter and AC input currents, when the ACinput current exceeds the limit value, the current controllerintegration reset circuit producing a signal.

The current control means abruptly reduces the absolute values of theintegrating elements when an AC input current exceeds a limit value, andwhen the integrating elements of the current control means are differentin polarity from the AC reference signals whose phases correspond tothose of the integrating elements and the electrical quantities of theinput currents accumulated in the integrating elements are in excess ofa predetermined value.

According to an additional aspect of the invention, there is provided acontrol device for a PWM controlled converter having voltage controlmeans for comparing a voltage set value with a detecting value of a DCvoltage output from the PWM controlled converter, connected to an ACpower source, for controlling AC input currents supplied form the ACpower source, to thereby produce a current reference signal, ACreference signal outputting means for outputting AC reference signalssynchronized with the AC power source, current instruction means forproducing current instruction signals formed by varying the amplitudesof the AC reference signals output from the AC reference signaloutputting means in accordance with the current reference signal, andcurrent control means for producing control signals to the PWMcontrolled converter so that the AC input currents vary as instructed bythe current instruction signals, the improvement characterized in thatwhen an AC input current exceeds a predetermined limit value, thecurrent control means abruptly reduces the current reference signals.

In the control device, the current control means includes integratingelements, and when an AC input current exceeds a predetermined limitvalue, resets the integrating elements to zero (0).

Also in the control device, when an AC input current exceeds apredetermined limit value, the voltage control means varies a currentreference signal as defined by a time function of which an initial valueis the current reference signal smaller than the current referencesignal at least at the time point where the input current exceeds thelimit value.

When an AC input current exceeds a predetermined limit value, and whenthe integrating elements of the current control means are different inpolarity from the AC reference signals whose phases correspond to thoseof the integrating elements and the electrical quantities of the inputcurrents accumulated in the integrating elements are in excess of apredetermined value, the current control means reduces the currentreference signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an arrangement of an embodiment 1 of acontrol device for a PWM controlled converter according to the presentinvention.

FIG. 2 is a diagram showing the details of an arrangement of an R-phasecurrent controller shown in FIG. 1.

FIG. 3 is a diagram showing the details of an arrangement of a currentcontrol switch device shown in FIG. 1.

FIG. 4 is a vector diagram of voltage and current in the power sourceside of the device shown in FIG. 1.

FIG. 5 is an explanatory diagram showing a relationship between controlsignals to the PWM controlled converter and a carrier wave signal.

FIG. 6 is a diagram showing an arrangement of an embodiment 2 of acontrol device for a PWM controlled converter according to the presentinvention.

FIG. 7 is a flow chart useful in explaining an operation of theembodiment 2 shown in FIG. 6.

FIG. 8 is a diagram showing an arrangement of an embodiment 3 of acontrol device for a PWM controlled converter according to the presentinvention.

FIG. 9 is a diagram showing an arrangement of an embodiment 4 of acontrol device for a PWM controlled converter according to the presentinvention.

FIG. 10 is a circuit diagram showing an arrangement of a voltagedetecting circuit shown in FIG. 9.

FIG. 11 is a flow chart showing an operation of the embodiment 4 shownin FIG. 9.

FIG. 12 is a circuit diagram showing another arrangement of the voltagedetecting circuit shown in FIG. 9.

FIG. 13 is a diagram showing an arrangement of an embodiment 5 of acontrol device for a PWM controlled converter according to the presentinvention.

FIG. 14 is a diagram showing a detailed arrangement of a currentcontroller integration reset circuit in the embodiment 5 shown in FIG.13.

FIG. 15 is a diagram useful in explaining an operation of the embodiment5 shown in FIG. 13.

FIG. 16 is a diagram showing an arrangement of an embodiment 6 of acontrol device for a PWM controlled converter according to the presentinvention.

FIG. 17 is a diagram useful in explaining an operation of the embodiment6 shown in FIG. 16.

FIG. 18 is a diagram showing an arrangement of an embodiment 7 of acontrol device for a PWM controlled converter according to the-presentinvention.

FIG. 19 is a diagram showing a detailed arrangement of a currentcontroller integration reset circuit in the embodiment 7 shown in FIG.18.

FIG. 20 is a diagram showing an arrangement of an embodiment 8 of acontrol device for a PWM controlled converter according to the presentinvention.

FIG. 21 is a diagram showing a detailed arrangement of a currentcontroller integration reset circuit in the embodiment 8 shown in FIG.20.

FIG. 22 is a diagram useful in explaining an operation of the embodiment8 shown in FIG. 20.

FIG. 23 is a diagram showing an arrangement of an embodiment 9 of acontrol device for a PWM controlled converter according to the presentinvention.

FIG. 24 is a diagram useful in explaining an operation of the embodiment9 shown in FIG. 23.

FIG. 25 is a diagram showing an arrangement of an embodiment 10 of acontrol device for a PWM controlled converter according to the presentinvention.

FIG. 26 is a diagram showing the detail of an arrangement of a peakvalue instruction signal switch device in the embodiment 10 shown inFIG. 24.

FIG. 27 is a diagram showing an arrangement of an embodiment 11 of acontrol device for a PWM controlled converter according to the presentinvention.

FIG. 28 is a diagram showing an arrangement of a conventional controldevice for a PWM controlled converter.

FIG. 29 is a diagram showing the detail of an arrangement of aconventional R-phase current controller.

FIG. 30 is a diagram showing the detail of an arrangement of aconventional voltage detecting circuit.

FIG. 31 is a waveform diagram showing the waveforms of input currents tothe PWM controlled converter before the converter starts its controloperation.

FIG. 32 is a waveform diagram showing the waveforms of the power sourcevoltage and currents of a control device for a PWM controlled converter,and a voltage of the PWM controlled converter.

FIG. 33 is a waveform diagram showing the waveforms of the voltages andcurrents at key portions when an instantaneous power interrupt takesplace in a conventional control device for a PWM controlled converter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be described hereunder.

Embodiment 1

FIG. 1 is a diagram showing one of the embodiments of a control devicefor a PWM-controlled converter according to the present invention. Inthe figure, reference numeral 1 designates a 3-phase AC power source 1;2, a PWM controlled converter which converts an AC power received fromthe 3-phase AC power source 1 into a DC voltage by controlling the ACcurrent of the received AC power, and outputs the converted DC voltage;201 to 206, switching elements which are transistors; and 207 to 212,circulating diodes.

Numeral 3 designates reactors connected between the 3-phase AC powersource 1 and the PWM controlled converter 2; 4, a smoothing condenserfor absorbing a pulsating component contained in an output current ofthe PWM controlled converter 2; 5, a load unit such as an invertor; 6, avoltage setter for outputting a voltage setting signal for setting a DCvoltage output from the PWM controlled converter 2; and 7b, a voltagedetecting circuit which detects a DC voltage output from the PWMcontrolled converter 2.

Numeral 8 indicates a subtractor for calculating a deviation of avoltage detecting signal detected by and output from the voltagedetecting circuit 7b from a voltage setting signal set by and outputfrom the voltage setter 6; 9d, a voltage controller which includes aproportional control calculating element and a proportional integrationcalculating element, and proportional integration (PI) controls adeviation of a voltage detecting signal output from the subtractor 8from the voltage setting signal, and forms voltage control means,together with the subtractor 8; 10, an AC voltage detector for detectingan AC voltage from the 3-phase AC power source 1; 11, a unit sine wavegenerator for generating R-phase and T-phase unit sine waves, which aresynchronized with R-phase and T-phase voltages, from an AC voltagedetecting signal detected by the AC voltage detector 10, and formsreference AC signal outputting means, together with the AC voltagedetector 10. Numerals 12 and 13 designate multipliers for multiplying apeak value instruction signal of an input current received from thevoltage controller 9d by R-phase and T-phase unit sine wave signalsreceived from the unit sine wave generator 11, and outputs R-phase andT-phase input current instruction signals. The multipliers form acurrent instruction means.

Numerals 14 and 15 represent current detectors for detecting currents ofR-phase and T-phase input to the PWM controlled converter 2; 16 and 17,subtractors for producing a deviation of an input current detectingsignal of R-phase output from the current detector 14 from an inputcurrent instruction signal of R-phase output from the multiplier 12 anda deviation of an input current detecting signal of T-phase output fromthe current detector 15 from an input current instruction signal ofT-phase output from the multiplier 13; 18a and 19a, R- and T-phasecurrent controllers which include proportional control calculatingelements and proportional integration calculating elements, and controlthe deviations of the T-phase input current detecting signals from theR-phase input current instruction signals, to thereby output an R-phasecontrol signal and a T-phase control signal; and 20, a subtractor forsubtracting from zero the R- and T-phase control signals output from theR- and T-phase current controllers 18a and 19a.

Numeral 21 designates a carrier wave oscillator; 22, 23 and 24 designatecomparators for comparing the amplitudes of R-, S- and T-phase controlsignals with a carrier wave signal to output pulse-width modulatedsignals; 25, a gate circuit for outputting signals to turn on and offthe switching elements 201 to 206 of the PWM controlled converter 2 inaccordance with R-, S- and T-phase pulse-width modulated signals; and26, a current control switch device for controlling the integratingelements of the R- and T-phase current controllers 18a and 19a to bezero. Current control means is made up of the current detectors 14 and15, the subtractors 16 and 17, R- and T-phase current controllers 18aand 19a, subtractor 20, carrier wave oscillator 21, comparators 22, 23and 24, gate circuit 25, and the current control switch device 26. Inthe figure, the circuit components 1 to 17, and 20 to 25 are the same asthe corresponding ones already stated in the prior art discussion.

FIG. 2 is a diagram showing the detail of an arrangement of the R-phasecurrent controller 18a shown in FIG. 1. In FIG. 2, reference numerals121 to 123 designate fixed resistors of resistance values r1 to r3; 124,a capacitor of capacitance C1; 125, an operational amplifier; 126 and127, positive and negative voltage input terminals of a control powersource for driving the operational amplifier 125; 128, an analog switchconnected across the capacitor 124; 129, a control input terminal forreceiving a control signal for controlling a switching operation of theanalog switch 128; 130, an input terminal of the R-phase currentcontroller 18a for receiving a deviation signal from the subtractor 16;and 131, an output terminal of the R-phase current controller 18a foroutputting an R-phase control signal to the comparator 22. The T-phasecurrent controller 19a is similarly constructed.

FIG. 3 is a diagram showing the detail of an arrangement of the currentcontrol switch device 26 shown in FIG. 1. In FIG. 3, reference numerals141 to 144 indicate fixed resistors of resistance values r11 to r14;145, a capacitor of capacitance C11; 146, a switch; 147, a comparator;and 148, an output terminal for outputting a signal for controlling theR- and T-phase current controllers 18a and 19a.

Proceeding with the operation description of the embodiment 1, theoperation principle will be described. FIG. 4 is a vector diagram ofvoltage and current in the power source side of the device shown inFIG. 1. eS represents a power source voltage vector of the 3-phase ACpower source 1; VC, an AC side voltage vector of the PWM controlledconverter 2, VL, a voltage vector VL of the reactor 3; and IS, a vectorof an input current supplied from the power source. To control the inputcurrent IS so as to be in phase with the power source voltage (highpower factor), the reactor voltage VL must lead the AC side voltage VCof the PWM controlled converter 2 by 90°. Therefore, the AC side voltageVC is always larger than the power source voltage eS.

Description will be given about a relationship between the DC sidevoltage V DC and an effective value (denoted as V RMS for ease ofexplanation) of an AC side line voltage as a magnitude of the AC sidevoltage vector. In case where the amplitudes of R-, S- and T-phasecontrol signals SR*, SS* and ST* are smaller than the amplitude Tx ofthe carrier wave signal Tx, if the waveforms of the R-, S-and T-phasecontrol signals SR*, SS* and ST* are sinusoidal, the waveforms of thevoltage fundamental wave components of those phases are also sinusoidal.In case where 1/2 of the DC side voltage V DC of the PWM controlledconverter 2 is the reference potential, ±(V DC/2) holds when the controlsignals SR*, SS* and ST* are equal in amplitude to the carrier wavesignal Tx. Hence, in order that the control signals SR*, SS* and ST* areequal in amplitude to the carrier wave signal Tx, a relationship betweenthe effective value V RMS of the line voltage and the DC side voltage VDC must satisfy the following condition given by an expression (1)

    V RMS V DC/2/ 2×3                                    (1)

Rearranging the expression (1), we have ##EQU1##

From the above expressions, in order that the output voltages of thosephases are output having the fundamental waveform components while beingunsaturated, the DC side voltage V DC of the PWM controlled converter 2must be at least 1.64 times as large as the AC side line voltageeffective value V RMS. If the DC side voltage V DC is smaller than thevalue that is 1.64 times as large as the AC side line voltage effectivevalue V RMS, viz., in a region where the amplitudes of the controlsignals SR*, SS* and ST* are larger than the amplitude of the carrierwave signal Tx, the output voltage is limited within ±(V DC/2) in aregion where the control signals exceed the carrier wave signal Tx.

In the conventional control device for a PWM controlled converter, theR- and T-phase control signals SR* and ST* are calculated by the PIcurrent controllers, and the S-phase control signal SS* is obtained asSS*=(-SR*-ST*), which follows from a formula SR*+SS*+ST*=0. Therefore,when the amplitudes of the control signals exceed each amplitude of thecarrier wave signal-Tx, as shown in FIG. 5, the control signals of theremaining phases automatically change, so that the line voltages arecontrolled as instructed by the instruction values. Accordingly, theinput currents are satisfactorily controlled only when the controlsignals of the respective phases are within a 60° saturation, viz., atime duration where the amplitudes of the control signals exceed theamplitude of the carrier wave signal Tx is within 60°, the followingcondition for the AC side line voltage effective value V RMS and the DCside voltage V DC is expressed by an expression (3)

    V RMS≦V DC/2×                                 (3)

Rearranging the expression (3), we have ##EQU2##

When the control device is started up in a state that the PWM controlledconverter 2 is not controlled by the signals from the gate circuit 25,but the load unit 5 is operating, for example, in a load active statethat the load unit 5 is operating, the DC side voltage V DC of the PWMcontrolled converter 2 is lower than the line voltage peak value(greater than the line voltage by the square root of 2) by the voltagedrop across the reactor 3. The effective value V RMS of the AC side linevoltage of the PWM controlled converter 2 must be larger than theeffective value of the line voltage of the 3-phase AC power source 1 asdescribed above. Therefore, the DC side voltage V DC is below the valuegiven by the expression (4). In this case, an attempt to control theinput currents so as to be in phase with the power source voltage (highpower factor) as instructed by the instruction fails since the AC sideline voltage of the PWM controlled converter 2 is insufficient inamplitude and a region in which control is not possible is present inthe AC side line voltage of the PWM controlled converter 2. As a result,the actual current value is not coincident with the current instructionvalue.

For the R- and T-phase control signals SR* and ST*, produced through thePI controlling of the deviations output from the subtractors 16 and 17by the R- and T-phase current controllers 18a and 19a, the deviationsthereof are progressively accumulated in the integrators, and with theaccumulation, grow in the positive or negative direction up to thesaturation voltages of the operational amplifiers, and are fixed at thesaturation voltages. Further, the S-phase control signal SS* is obtainedas SS*=(-SR*-ST*), and hence the control signal is also fixed at a valuewhen the control signals SR* and ST* are saturated. As a result, thecontrol device cannot control the input currents of three phases.

If the proportional control is used for the control scheme of each ofthe current controllers 18a and 19a, if the DC side voltage V DC dropsand the current instruction value is coincident with the actual currentvalue, the R- and T-phase control signals SR* and ST* have valuesobtained by proportionally multiplying the deviations. Therefore, theoperational amplifiers are not saturated, and the voltage of at leastone phase is controllable. In the R- and T-phase current controllers 18aand 19a based on the proportional control, a steady deviation is causedbetween the current instruction value and the actual current value.

Accordingly, the embodiment 1 proposes a control device for a PWMcontrolled converter which operates in a proportional control mode onlyat the time of starting where the control device is apt to fail incontrolling the voltages of three phases since the proportionalintegration control saturates the operational amplifiers.

An operation of the embodiment 1 shown in FIGS. 1 through 3 will bedescribed. A detecting value V DC of a DC voltage detected by thevoltage detecting circuit 7b and a set value V DC* set by the voltagesetter 6 are input to the subtractor 8 where the eV (deviation)=V DC -VDC* is calculated. The obtained deviation eV is input to the voltagecontroller 9d where it is PI-controlled so as to reduce the deviation tozero and produces a peak value instruction signal I PEAK* of the inputcurrent. The peak value instruction signal I PEAK* is applied to themultipliers 12 and 13 where it is multiplied by the unit sine wavesignals of R-phase and T-phase derived from the unit sine wave generator11. The R- and T-phase unit sine wave signals are unit sine wavesignals, i.e., reference AC signals, synchronized with the R- andT-phase voltages of the 3-phase AC power source 1, and are generated bya current reference signal generator constituting the unit sine wavegenerator 11, which receives an AC voltage of the 3-phase AC powersource 1 detected by the AC voltage detector 10. The multipliers 12 and13 produce an R-phase input current instruction signal iR* and a T-phaseinput current instruction signal iT*, respectively.

The R-phase input current instruction signal iR* as an output signal ofthe multiplier 12 and an R-phase input current detecting signal iR as anoutput signal of the current detector 14 are applied to the subtractor16 which calculates eiR (deviation)=iR* -iR and outputs the result ofthe calculation. Similarly, the T-phase input current instruction signaliT* as an output signal of the multiplier 13 and a T-phase input currentdetecting signal iT as an output signal of the current detector 15 areapplied to the subtractor 17 which calculates eiT (deviation) =iT*-iTand deviations eiR and eiT are applied to the R-phase current controller18a and the T-phase current controller 19a, respectively. In each of thecontrollers 18a and 19a, a proportional control mode or a proportionalintegration mode is selected by the current control switch device 26.

In the current control switch device 26, constructed as shown in FIG. 3,the switch 146 is turned on upon receipt of a control start signal or adrive signal. Then, a voltage at the positive input terminal of thecomparator 147 rises at a time constant determined by the fixed resistor142 and the capacitor 145. The output of the comparator 147 is at an "L"level during a period that the voltage at the positive input terminal ofthe comparator 147 is smaller than the voltage at the negative inputterminal. When the voltage at the positive input terminal of thecomparator gently rises through the fixed resistor 142 and the capacitor145, and exceeds the voltage at the negative input terminal of thecomparator, which is set by the fixed resistors 143 and 144, the outputof the comparator is at an "H" level.

The output signal of the comparator 147 is applied as the output signalof the current control switch device 26 to the R- and T-phase currentcontrollers 18a and 19a, through the output terminal 148. In the R-phasecurrent controller 18a constructed as shown in FIG. 2, when an inputsignal at the control input terminal 129 is at an "L" level, the analogswitch 128 is placed in an on state, so that the capacitor 124 isshorted. In this state, an R-phase current deviation eiR that comes inthrough the input terminal 130 of the R-phase current controller 18aundergoes only a proportional control as given by expression (5), andthe result of the proportional control is output as an R-phase controlsignal SR from the output terminal 131.

    SR*=-K1×eiR                                          (5)

where K1=r2/r1.

When the input signal on the control input terminal 129 is at an "H"level, the analog switch 128 is placed in an on state. An R-phasecurrent deviation eiR, which comes in through the input terminal 130 ofthe R-phase current controller 18a, is PI controlled according to thefollowing expression (6) and the result of the PI controlling is outputas an R-phase control signal SR* through the output terminal 131 of theR-phase current controller.

    SR*=-K1×(1+1/(S×T))×eiR                  (6)

where K1=r2/r1

T=C1×C2

S=differential operator

The T-phase current controller 19a operates in a similar way. When aninput signal on the control input terminal 129 is at an "L" level, thecurrent deviation eiT undergoes a proportional control. When it is at an"H" level, the current deviation undergoes a proportional integrationcontrol, and the resultant signal is output as a T-phase control signalST* from the T-phase current controller. An S-phase control signal SS isformed by the subtractor 20 in a manner that the R- and T-phase controlsignals SR* and ST* are reduced from 0. The control signals SR*, SS* andST* as the output signals of the R-phase current controller 18a, thesubtractor 20 and the T-phase current controller 19a are applied to thecomparators 22, 23 and 24, respectively. In the comparators, thosesignals are each compared in amplitude with a carrier wave signal oftriangle waves output from the carrier wave oscillator 21. The resultantsignals are output in the form of pulse width modulated (PWM) signals.

These PWM signals are input to the gate circuit 25 which in turn outputscontrol signals to the PWM controlled converter 2. In the converter,under control of the control signals, the switching elements 201 to 206are controlled so that the DC voltage detecting value V DC of the PWMcontrolled converter 2 is equal to the set value V DC* set by thevoltage setter 6. Further, the input currents iR, iS and iT of R-, S-and T-phase are equal to their instruction signals iR*, iS* and iT*.

In the embodiment 1, the R- and T-phase currents are detected for theconverter control. Any other combinations of those three phase currentsmay be used for the same purposes.

In the control device for a PWM controlled converter according to theembodiment 1, the current control means produces control signals basedon a proportional control for a predetermined period after the controlstarts, and produces other control signals based on a proportionalintegration control after the predetermined period is terminated.Specifically, at starting the proportional-control basis control signalsare used for controlling the PWM controlled converter for apredetermined period, and after the predetermined period terminates, theproportional-integration-control basis control signals are used forcontrolling the PWM controlled converter. Therefore, no overcurrentproblem arises, and a good control of the input currents is secured.

Embodiment 2

FIG. 6 is a diagram showing an arrangement of another embodiment of acontrol device for a PWM controlled converter according to the presentinvention. In FIG. 6, reference numeral 27 designates a current controlselect-level setter, and numeral 28, a comparator. The comparatorcompares a set value V SW. detected by the current control select-levelsetter 27 with a DC voltage detecting value V DC detected by the voltagedetecting circuit 7b, and produces signals for controlling the R- andT-phase current controllers 18a and 19a. The remaining construction ofthe control device is substantially the same as of the embodiment shownin FIG. 1.

In the embodiment shown in shown in FIG. 1, the R- and T-phase currentcontrollers 18a and 19a each produce a control signal based on aproportional control for a predetermined period set by the currentcontrol switch device 26 after a controlling operation starts, viz.,during a period determined by a time constant determined by the fixedresistor 142 and the capacitor 145, and produce a control signal basedon a proportional integration control after the predetermined periodterminates. The embodiment shown in FIG. 6 includes the combination ofthe current control select-level setter 27 and the comparator 28, whichperforms the following signal selective operation. When a DC voltagedetecting value V DC detected by the voltage detecting circuit 7b isbelow a set value V SW* preset by the current control select-levelsetter 27, the R- and T-phase current controllers 18a and 19a produceproportional-control basis control signals. When the value V DC is abovethe set value V SW*, the R- and T-phase current controllers 18a and 19aproduce proportional-integration-control basis control signals.

More specifically, a set value V SW* as an output signal of the currentcontrol select-level setter 27 and a DC voltage detecting value V DCdetected through the voltage detecting circuit 7b are applied to thecomparator 28. Before the DC voltage V DC exceeds the set value V SW*,the R- and T-phase current controllers 18a and 19a each produce an "L"level signal as a control signal for the proportional control. After theDC voltage V DC exceeds the set value V SW*, the R- and T-phase currentcontrollers 18a and 19a each produce an "H" level signal as a controlsignal for the proportional integration control. The R-phase currentcontroller 18a performs a proportional control on the R-phase currentdeviation eiR applied thereto when the input signal on the controlinput-terminal 129 shown in FIG. 2 is at an "L" level, and performs aproportional integration control on the same when the input signal is atan "H" level, and produces an R-phase control signal SR at the inputterminal 130 thereof. The T-phase current controller 19a also performs aproportional control on the R-phase current deviation eiT appliedthereto when the input signal on the control input terminal is at an "L"level, and performs a proportional integration control on the same whenthe input signal is at an "H" level, and produces a T-phase controlsignal TR* at the input terminal 130.

The operation of the embodiment shown in FIG. 6 will be described withreference to a flow chart shown in FIG. 7. When the control device isstarted up, or the control operation starts, the R- and T-phase currentcontrollers 18a and 19-a are set in a proportional control mode in astep S1. In the next step S2, a set-value V SW* as an output signal ofthe current control select-level setter 27 and a DC voltage detectingvalue V DC detected through the voltage detecting circuit 7b arecompared by the comparator 28. If V DC <V SW*, the current controllersholds the proportional control mode set in the step S1. If the step S2determines that V DC >V SW*, a step S3 is executed to place the R- andT-phase current controllers 18a and 19a in a proportional integrationcontrol. As already described referring to the expression (4), when theDC side voltage V DC is at least approximately 1.41 times as large asthe AC side line voltage effective value V RMS, the voltage control canbe performed as instructed by an instruction value. Therefore, thesetting of the set value V SW* within the range of the values above thatvalue but below the set value V DC* of the voltage setter 6 will do.

In the control device for a PWM controlled converter of the embodiment2, current control means produces control signals based on aproportional control before a detecting value of the DC voltage of thePWM controlled converter exceeds a predetermined value, and producesother control signals based on a proportional integration control aftera detecting value of the DC voltage of the PWM controlled converterexceeds a predetermined value. Therefore, a proportional control mode isswitched to a proportional integration control mode and vice versa at anoptimum switching timing. Particularly at starting, a good input currentcontrol can be carried out without causing the overcurrent problem, forexample. Additionally, the proportional control period possibly causinga steady deviation may easily be minimized in consideration of theoverall circuit arrangement.

Embodiment 3

FIG. 8 is a diagram showing an arrangement of an embodiment 3 of acontrol device for a PWM controlled converter according to the presentinvention. In FIG. 8, reference numeral 29 designates a subtractor whichsubtracts from 0 a deviation of an R-phase input current detectingsignal iR from an R-phase input current instruction signal iR* that isoutput from the subtractor 16, and a deviation from a R-phase inputcurrent detecting signal iT from a T-phase input current instructionsignal iT* that is output from the subtractor 17, and outputs the resultof the subtraction in the form of a deviation of an input currentdetecting signal from an S-phase input current instruction signal.Numerals 30 and 31 indicate integrators. The integrator 30 integratesthe product of multiplying by a coefficient a deviation of an R-phaseinput current detecting signal iR from an R-phase input currentinstruction signal iR* that is output from the subtractor 16, andoutputs the result of the integration. The integrator 31 integrates theproduct of multiplying a coefficient by a deviation from a R-phase inputcurrent detecting signal iT* from a T-phase input current instructionsignal iT that is output from the subtractor 17, and outputs the resultof the integration. Numerals 32 to 34 represent coefficient multipliersfor multiplying by coefficients the deviations of current detectingsignals from the R-, S- and T-phase input current instruction signalsoutput from the subtractors 16, 29 and 17, respectively.

Reference numeral 35 designates a subtractor which receives theintegrating values of the R- and T-phase current deviations output fromthe integrators 30 and 31, and subtracts these integrating values fromzero (0). Numerals 36, 37 and 38 designate adders. The adder 36 addstogether the output signals of the coefficient multiplier 32 and theintegrator 30 to produce an R-phase control signal SR*. The adder 37adds together the output signals of the coefficient multiplier 33 andthe subtractor 35 to produce an S-phase control signal SS*. The adder 38adds together the coefficient multiplier 34 and the integrator 31 toproduce a T-phase control signal ST*. The remaining arrangement of thepresent embodiment is substantially the same as the arrangement of FIG.1 or 6. Like reference numerals are used for designating like equivalentportions in those embodiments already described.

In the embodiment of FIG. 1 or 6, the R- and T-phase current controlmeans of R- and T-phase produce control signals for transmission to thePWM controlled converter while switching its operation mode from theproportional control mode to the proportional integration control mode.In the embodiment shown in FIG. 8, the product of multiplying adeviation of the R-phase AC input current from the R-phase input currentinstruction signal output from the multiplier 12 constituting thecurrent control means by coefficients is integrated, and the product ofmultiplying a deviation of the T-phase input current from the T-phaseinput current instruction signal output from the multiplier 13 alsoconstituting the current control means is integrated, and the results ofthe integrations are output as first R- and T-phase output signals. Thesign inverse values of those first R- and T-phase output signals areadded together to form a first S-phase output signal. Further, theproducts of multiplying the deviations of the AC input currents from theinput current instruction signals by the coefficients are output assecond output signals of the respective phases. The sums of the firstand second output signals of the respective phases are output in theform of control signals for the PWM controlled converter.

An operation of the embodiment shown in FIG. 8 will be described. A DCvoltage detecting value V DC detected through the voltage detectingcircuit 7b and a set value V DC* set by the voltage setter 6 are inputto the subtractor 8 where a deviation eV therebetween is calculated;eV=V DC*-V DC . The deviation eV is input to the voltage controller 9d.The controller PI controls the deviation so that it approaches zero (0),and produces a peak value instruction signal I PEAK* of the AC inputcurrent. The peak-value instruction signal I PEAK* is input to themultipliers 12 and 13 which in turn multiply the peak value instructionsignal I PEAK* by the R- and T-phase unit sine wave signals derived fromthe unit sine wave generator 11. The R- and T-phase unit sine wavesignals are unit sine wave signals, i.e., reference AC signals,synchronized with the R- and T-phase voltages of the 3-phase AC powersource 1, and are generated by a current reference signal generatorconstituting the unit sine wave generator 11, which receives an ACvoltage of the 3-phase AC power source 1 detected by the AC voltagedetector 10.

An R-phase input current instruction signal iR* as an output signal ofthe multiplier 12 and an R-phase input current detecting signal iR as anoutput signal of the current detector 14 are input to the subtractor 16.In turn, the subtractor calculates a deviation eiR by eiR=iR*-iR, andoutputs the result of the calculation. Similarly, a T-phase inputcurrent instruction signal iT* as an output signal of the multiplier 13and an R-phase input current detecting signal iT as an output signal ofthe current detector 15 are input to the subtractor 17. The subtractorcalculates a deviation eiT by the formula eiT=iT-iT. Further, an S-phasecurrent deviation eiS is calculated by the formula eiR+eiS+eiT=0. Thecurrent deviations eiR and eiT are input to the subtractor 29. In turn,the subtractor subtracts these deviations from zero (0) and produces theresult of the calculation as an S-phase current deviation eiS.

The R-phase current deviation eiR is input to the integrator 30 and thecoefficient multiplier 32. A proportional term and an integration termof the R-phase current control as the outputs of the integrator 30 andthe multiplier 32 are added together, by the adder 36, into an R-phasecontrol signal SR. The T-phase current deviation eiT is input to theintegrator 31 and the coefficient multiplier 34. A proportional term andan integration term of the T-phase current control as the outputs of theintegrator 31 and the multiplier 34 are added together, by the adder 38,into a T-phase control signal ST*. The output signal of the integrator30 as the integration term of the R-phase current control and the outputsignal of the integrator 31 as the integration term of the T-phasecurrent control are input to the subtractor 35. The subtractor 35subtracts those output signals from zero (0) to form an S-phaseintegration term. The output signal of the subtractor 35 and an S-phaseproportional term, which is formed by multiplying an S-phase currentdeviation eiS as the output signal of the subtractor 29 by thecoefficient multiplier 33, are input to the adder 37. The adder addstogether the S-phase integration term and the S-phase proportional termto generate an S-phase control signal SS*.

The R-, S- and T-phase control signals SR*, SS* and ST* as the outputsignals of the adders 36, 37 and 38 are applied to the comparators 22,23 and 24. By the comparators, those control signals are compared inamplitude with a carrier wave signal of a triangle wave that is outputfrom the carrier wave oscillator 21, and the results of the comparisonsare output in the form of pulse width modulation signals. These PWMsignals are input to the gate circuit 25 which in turn outputs controlsignals to the PWM controlled converter 2. In the converter, undercontrol of the control signals, the switching elements 201 to 206 arecontrolled so that the DC voltage detecting value V DC of the PWMcontrolled converter 2 is equal to the set value V DC* set by thevoltage setter 6, and further the input currents iR, iS and iT of R-, S-and T-phase are equal to their instruction signals iR*, iS* and iT*.

As described above, in the PWM controlled converter according to theembodiment 3, the current control means multiplies the deviations of theAC input currents from the R- and T-phase current instruction signalsoutput from the multipliers 12 and 13, which form current instructionmeans, by the coefficients, integrates the results of themultiplications, and outputs the results of the integrations in the formof first R- and T-phase output signals. The sign inverse values of thosefirst R- and T-phase output signals are added together to form a firstS-phase output signal. Further, the products of multiplying thedeviations of the AC input currents from the input current instructionsignals are output as second output signals of the respective phases.The sums of the first and second output signals of the respective phasesare output in the form of control signals for the PWM controlledconverter. In such a construction, the proportional control is performedon the S-phase. Therefore, at starting no overcurrent problem arises.Even when the DC side voltage V DC drops by a load variation, noovercurrent problem arises, and good current control is secured.

Embodiment 4

FIG. 9 is a diagram showing an arrangement of an additional embodimentof a control device for a PWM controlled converter according to thepresent invention. In FIG. 9, reference numeral 7a is representative ofa voltage detecting circuit 7a for detecting a DC voltage output fromthe PWM controlled converter 2, and it forms a DC voltage detectingmeans. Numeral 40 represents a memory circuit for storing relationshipsbetween the known values of voltages applied to the voltage detectingcircuit 7a and the voltage values detected by the voltage detectingcircuit 7a; and numeral 41, a voltage-setting-signal correction circuitwhich corrects a voltage setting signal set and output by the voltagesetter 6 while referring to the relationships stored in the memorycircuit 40, and outputs the corrected one to the subtractor 8. Thememory circuit 40, the voltage setting-signal correction circuit 41, andthe voltage setter 6 form voltage instruction outputting means. For theremaining construction, like or equivalent portions are designated bylike reference numerals in FIG. 1 showing the embodiment 1, forsimplicity.

FIG. 10 is a circuit diagram showing a detailed arrangement of a voltagedetecting circuit 7a for detecting a DC voltage V DC in the controldevice shown in FIG. 9. In FIG. 10, reference numeral 751 indicates aninput terminal connected to the positive potential of the smoothingcondenser 4; and 752 and 753 indicate fixed resistors for dividing theDC voltage V DC, one end of the fixed resistor 753 being connected tothe negative potential of the smoothing condenser 4. Reference numeral754 designates an insulating amplifier; 755 to 756, fixed resistors;757, an operational amplifier; and 758, an output terminal foroutputting a DC voltage detecting value V DC to the subtractor 8.

In the thus arranged voltage detecting circuit 7a, a DC voltage V DC isdivided, by the fixed resistors 752 and 753, into a voltage within arange of voltage values that can be accepted by the insulating amplifier754. The insulating amplifier 754 detects the divided voltage in aninsulating manner. The operational amplifier 757 amplifies the detectedvoltage to a proper level of the voltage, and outputs it from the outputterminal 758. The circuit thus arranged is a basic circuit generallyused for adjusting an offset and a gain of the voltage detecting circuitby an operational amplifier. The present voltage detecting circuit isdifferent from the voltage detecting circuit 7b shown in FIG. 28 in thatthe former does not include a variable resistor for adjusting the offsetand gain errors of the voltage detecting value.

The operation of the embodiment 4 shown in FIGS. 9 and 10 will bedescribed with reference to a flow chart shown in FIG. 11. As shown inthe FIG. 11 flow chart, adjusting known voltage values and detectingvalues of the DC voltage detected by the voltage detecting circuit 7aare first stored in a corresponding fashion into the memory circuit 40.

More specifically, in a step S101 a known voltage V1 is applied to thevoltage detecting circuit 7a, from an outside circuit. The known voltagemay be applied to the voltage detecting circuit in a manner that theswitching elements 201 to 206 of the PWM controlled converter 2 areturned off, and in this state an AC voltage of the 3-phase AC powersource 1 is converted into a DC voltage by the circulating diodes 207 to212 of the PWM controlled converter 2, and the DC voltage is applied tothe voltage detecting circuit. Alternatively, the known voltage may beapplied to the voltage detecting circuit 7a, from a DC power source thatis provided outside the control device.

In a step S102, the known voltage V1 applied to the voltage detectingcircuit 7a and a voltage value V1 detected by the voltage detectingcircuit 7a when it receives the known voltage V1 are stored into thememory circuit 40.

In a step S103, another known voltage V2 that is different from theknown voltage V1 is applied to the voltage detecting circuit 7a. In astep S104, the second known voltage V2 that is applied to the voltagedetecting circuit 7a and a voltage value V2 detected by the voltagedetecting circuit 7a when it receives the second known voltage V2 arestored into the memory circuit 40.

In a step S105, an offset error or a gain error of the voltage detectingcircuit is corrected according to expressions (7) and (8) while usingthe applied known voltages V1 and V2 and the detected voltage values V1and V2. Voltage setting values are corrected so that the DC voltage ofthe PWM controlled converter 2 has a desired voltage value, andcorrection coefficients A and B to be used for voltage setting signalsare calculated.

    A=(V2 -V1 )/(V2-V1)                                        (7)

    B=(V1 ×V2-V2 ×V1)/(V2-V1)                      (8)

    V DC**=A×V DC*+B                                     (9)

In step S106, the correction coefficients A and B are stored into thememory circuit 40. In this way, a voltage instruction value V DC* set bythe voltage setter 6 is corrected according to the expression (9) whileusing the correction coefficients A and B thus stored in the memorycircuit 40, and a voltage set signal V DC** is generated. Using thevoltage set signal V DC**, it is possible to correct the offset or gainerror of the voltage detecting circuit.

A sequence of the correcting operation is performed when the PWMcontrolled converter is installed or before a normal operation of theconverter starts, for example, when it is tested. The correctingoperation may be performed according to a program stored in a memory ofa microcomputer. Therefore, the volume that is attached to the voltagedetecting circuit for adjusting the offset or gain error of the voltagedetecting circuit 7a in the conventional device may be omitted. Further,the troublesome work for the offset or gain error correction iseliminated, and the operability of the control device is improved.

In the error correction method described above, the relationshipsbetween the known voltage values applied to the voltage detectingcircuit 7a and the detecting values are approximated by the linearfunctions, and by calculating the linear functions, and the correctioncoefficients A and B are obtained and stored. In a further errorcorrection method, the known voltage values and detecting values areincreased in number, the relationships between them are polygonallyapproximated, and the correction coefficients A and B are obtainedthrough a calculation and stored. This error correction method ensures afurther precise correction of those errors. When the voltage detectingcircuit 7a does not include a zero offset, the steps S103 and S104 maybe omitted. In this case, the error correction calculations areperformed with V2=0 and V2 =0. Conversely, when only the offset of thevoltage detecting circuit 7a is problematic, the step S101 is executedunder the condition that V1=0, and the steps S103 and S104 are omitted.In the error correction method described above, in calculating thecorrection coefficients A and B, the known voltage values and thevoltage values detected by the voltage detecting circuit 7a are storedin the memory circuit 40. Alternatively, the voltage values are storedinto a memory of a microcomputer for executing the sequence of theoperations, the correction coefficients are calculated, and thecalculated correction coefficients are stored into the memory circuit40.

A control operation that the control device for a PWM controlledconverter performs using the thus obtained correction coefficients A andB, will be described. A voltage instruction value V DC* set by thevoltage setter 6 is input to the voltage-setting-signal correctioncircuit 41. At adjusting, the voltage instruction value V DC* iscorrected using the correction coefficients A and B stored in advance inthe memory circuit 40, and the expression (9), and a voltage set signalV DC** formed after the correction of the voltage instruction value isoutput to the subtractor 8. Subsequently, the corrected voltage setsignal V DC** and the detecting value V DC output from the voltagedetecting circuit 7a are input to the subtractor 8 which in turn eV(deviation)=V DC**-V DC . The deviation eV is input to the voltagecontroller 9d which in turn performs a proportional integration on thedeviation and outputs a peak value instruction signal I PEAK* of theinput current. A control operation that the control device performsusing the thus obtained peak value instruction signal I PEAK* is similarto that of the embodiment shown in FIGS. 1, 6 and 8. Hence, no furtherdescription of it is given here.

As described above, in the control device for a PWM controlled converteraccording to the embodiment 4, the relationships between the values ofthe known voltages applied to the DC voltage detecting circuit and thevoltage values detected by the detecting circuit are stored in advance.The voltage instruction outputting means corrects the detection errorsof the DC voltage by using the stored voltage relationships so that anactual DC voltage of the PWM controlled converter is settled down at adesired value. Therefore, there is eliminated the use of the variableresistor, for example, for compensating for the offset or gain error ofthe voltage detecting circuit. Hence, troublesome compensating work iseliminated and the operability of the control device is improved.Further, the operation for adjusting the offset and gain errors caneasily be automated in the stage of manufacturing.

In the embodiment 4, known voltages are applied to the voltage detectingcircuit, from an exterior circuit. The relationships between the knownvoltage values and the voltage values detected by the voltage detectingcircuit are stored in advance. A voltage detecting circuit 7c as shownin FIG. 12 may be used instead of the above method. The voltagedetecting circuit shown in FIG. 12 uses a reference voltage generator asa means for providing known voltages.

FIG. 12 is a circuit diagram showing a detailed arrangement of thevoltage detecting circuit 7c for detecting a voltage V DC derived fromthe PWM controlled converter. In FIG. 12, reference numeral 761designates an input terminal connected to the positive potential of thesmoothing condenser 4; 762 and 763, fixed resistors for dividing the DCvoltage V DC, and the fixed resistor 763 is connected to the negativepotential of the smoothing condenser 4. Numerals 764 and 765 indicatereference voltage sources; 766, a signal selector for selecting an inputsignal to an insulating amplifier 767; 768 and 769, fixed resistors;770, an operational amplifier; and 771, an output terminal of thevoltage detecting circuit 7c.

In the voltage detecting circuit 7c shown in FIG. 12, at the time ofadjusting, the signal selector 766 is set at positions P2 and P3 so thatknown voltages are applied to the insulating amplifier from thereference voltage sources 764 and 765. And the correction coefficientsare calculated as in the above-mentioned manner. The voltages of thereference voltage sources 764 and 765 are directly applied to theinsulating amplifier 767. The DC voltage V DC is dropped to a voltagedefined by RL/(RH+RL) by means of the fixed resistors 762 and 763, andthen applied to the insulating amplifier 767. Therefore, the correctioncoefficients may be calculated and stored on the assumption that thevoltages obtained by multiplying the voltages of the reference voltagesources 764 and 765 by (RH+RL)/RL are the DC voltages V DC. In a normaloperation, as in the embodiment 4, a DC voltage V DC is divided, by thefixed resistors 762 and 763, into a voltage within a range of voltagevalues that can be accepted by the insulating amplifier 767. Theinsulating amplifier 767 detects the divided voltage in an insulatingmanner. The operational amplifier 770 amplifies the detected voltage toa proper level of the voltage, and outputs it from the output terminal771.

In the embodiment 4, it is necessary to apply a DC voltage at the samelevel as in a normal operation to the voltage detecting circuit. In thevoltage detecting circuit 7c shown in FIG. 12, since the voltagesobtained by multiplying the voltages of the reference voltage sources764 and 765 by (RH+RL)/RL may be considered to be the DC voltages V DC,the voltage source at a lower voltage level than the DC voltage V DC ina normal operation may be used for the reference voltage sources.

The circuit arrangement of the voltage detecting circuit 7c shown inFIG. 12 has the following additional useful effects as well as thoseeffects as of the embodiment 4. By constructing only the fixed resistors762 and 763 for dividing the DC voltage V DC coming in through the inputterminal 761 and the reference voltage sources 764 and 765 with highlyaccurate components and voltage sources, if the remaining circuitcomponents of the voltage detecting circuit 7c, for example, theinsulating amplifier 767 and the operational amplifier 770, are degradedin characteristics by aging, the characteristic degradation can becorrected without using other voltage sources.

Embodiment 5

FIG. 13 is a diagram showing an arrangement of an additional embodimentof a control device for a PWM controlled converter according to thepresent invention. In the figure, reference numeral 50 designates acurrent limit level setter for setting a limit value of an AC inputcurrent; and 51a, a current controller integration reset circuit forresetting the integrating elements of the R- and T-phase currentcontrollers 18a and 19a to zero (0). The current controller integrationreset circuit 51a receives signals from the current limit level setter50, and the current controllers 14 and 15, and outputs signals to theR-and T-phase current controllers 18a and 19a. In the remainingarrangement of the embodiment 5, like or equivalent portions aredesignated by like reference symbols in the embodiment 1 shown in FIG.1.

An operation of the embodiment shown in FIG. 13 will be described. A DCvoltage detecting value V DC detected through the voltage detectingcircuit 7b and a set value V DC set by the voltage setter 6 are input tothe subtractor 8 where a deviation eV therebetween is calculated; eV=VDC*-V DC . The deviation is input to the voltage controller 9d. Thecontroller PI controls the deviation so that it approaches zero (0), andproduces a peak value instruction signal I PEAK* of the AC inputcurrent. The peak value instruction signal I PEAK* is input to themultipliers 12 and 13 which in turn multiply the peak value instructionsignal I PEAK* by the R- and T-phase unit sine wave signals derived fromthe unit sine wave generator 11. The R- and T-phase unit sine wavesignals are unit sine wave signals, i.e., reference AC signals,synchronized with the R- and T-phase voltages of the 3-phase AC powersource 1, and are generated by a current reference signal generatorconstituting the unit sine wave generator 11, which receives an ACvoltage of the 3-phase AC power source 1 detected by the AC voltagedetector 10.

An R-phase input current instruction signal iR* as an output signal ofthe multiplier 12 and an R-phase input current detecting signal iR as anoutput signal of the current detector 14 are input to the subtractor 16.In turn, the subtractor calculates a deviation eiR by the formulaeiR=iR*-iR, and outputs the result of the calculation. Similarly, aT-phase input current instruction signal iT* as an output signal of themultiplier 13 and a R-phase input current detecting signal iT as anoutput signal of the current detector 15 are input to the subtractor 17.The subtractor calculates a deviation eiT by the formula eiT=iT*-iT. Thedeviations eiR and eiT are input to the R- and T-phase currentcontrollers 18a and 19a, respectively. The integrators, or theintegrating elements as the constituent elements of the R- and T-phasecurrent controllers 18a and 19a, are controlled by the currentcontroller integration reset circuit 51a.

FIG. 14 is a diagram showing a detailed arrangement of the currentcontroller integration reset circuit 51a. In the figure, referencenumerals 250 and 251 designate input terminals for receiving R- andT-phase input current detecting signals iR and iT from the currentdetectors 14 and 15; numeral 252, a subtractor for subtracting from zero(0) the R- and T-phase input current detecting signals iR and iT comingin through the input terminals 250 and 251; 253, a full-wave rectifierfor full-wave rectifying the R-, S- and T-phase input current detectingsignals iR, iS and iT and outputting the rectified ones; and 254, a setvalue I limit* as a limit value of the AC input power source limit levelthat is set and output by the current limit level setter 50. Further,numeral 255 indicates a comparator for comparing an input currentfull-wave rectified signal as an output signal of the full-waverectifier 253, viz., a maximum signal i P of the absolute values of theR-, S- and T-phase input current detecting signals iR, iS and iT, withthe set value I limit* of a current limit level coming through the inputterminal 254; numeral 256, a reset signal generator for generating asignal which resets to zero the integrating elements of the R- andT-phase current controllers 18a and 19a when the input current full-waverectified signal i P becomes larger than the current limit level setvalue I limit*; and 257, an output terminal for outputting a resetsignal derived from the reset signal generator 256.

When the R-, S- or T-phase input current, or the AC input current, islarger than the set value I limit* of the current limit level setter 50,the current controller integration reset circuit 51a resets theintegrating elements of the R- and T-phase current controllers 18a and19a to zero. As shown in FIG. 15, the R- and T-phase control signals SR*and ST* are caused to return quickly to a level which makes the AC inputcurrents to flow as instructed, to suppress the occurrence of a spikecurrent of the input current detecting signal. In FIG. 15, in a duration(A) where the power source is interrupted by an instantaneous powerinterruption and another duration (B) where the R-phase input currentdetecting signal iR is below the R-phase input current instructionsignal iR , the R-phase control signal SR is progressively accumulatedin the increasing direction of the R-phase input current detectingsignal iR. Its accumulation stops at a time (C) where the R-phase inputcurrent detecting signal iR is equal to the R-phase input currentinstruction signal iR*. Thereafter, at a time (D) where it exceeds theset value I limit* of the current limit level setter 50, the integratingelements are reset to zero (0), and the return of the control device toa normal operating state is quickened.

In FIG. 15, graphical description is given about the R-phase AC inputcurrent. The description is correspondingly applied to the control ofthe T-phase AC input current. The S-phase control signal SS* is formedin a manner that the subtractor 20 subtracts the R- and T-phase controlsignals SR* and ST* from 0. Therefore, the control of the S-phase ACinput current can be handled in a similar manner.

The control signals SR*, SS* and ST* as the output signals of theR-phase current controller 18a, the subtractor 20 and the T-phasecurrent controller 19a are applied to the comparators 22, 23 and 24. Bythe comparators, those control signals are compared in amplitude with acarrier wave signal of a triangle wave that is output from the carrierwave oscillator 21, and the results of the comparisons are output in theform of pulse width modulation signals. These PWM signals are input tothe gate circuit 25 which in turn outputs control signals to the PWMcontrolled converter 2. In the converter, under control of the controlsignals, the switching elements 201 to 206 are controlled so that the DCvoltage detecting value V DC of the PWM controlled converter 2 is equalto the set value V DC*, and further the input currents iR, iS and iT ofR-, S- and T-phase are equal to their instruction signals iR*, iS* andiT*.

In the embodiment 1, the R- and T-phase currents are detected for theconverter control. Any other combinations of those three phase currentsmay be used for the same purposes. It is evident that the presentinvention is applicable to the AC input current control of a singlephase.

In the above-mentioned embodiment, the integrating elements are reset tozero when the AC input current exceeds its limit value. Alternatively,when the AC input current exceeds its limit value, the absolute value ofthe integrating element may be abruptly reduced.

As described above, the control device for a PWM controlled converteraccording to the embodiment is constructed such that when an AC inputcurrent exceeds a limit value, the absolute values of the integratingelements of the current control means are abruptly reduced or reset to0. With such a construction, when an instantaneous power interruption,for example, takes place and the voltage of an AC power source drops oris interrupted for a short time, no overcurrent problem arises when thepower source returns to its normal state. Accordingly, the AC inputcurrent or currents can be satisfactorily controlled.

Embodiment 6

In the embodiment shown in FIG. 13, a set value I limit* of the currentlimit level is preset by the current limit level setter 50. In anembodiment of the invention shown in FIG. 16, a current limit offsetsetter 52 is used. An output signal I ost* of the current limit offsetsetter and an input current peak value instruction signal I PEAK* as theoutput signal are applied to an adder 53. The adder adds together thosereceived signals and outputs the result in the form of a set value Ilimit* of the current limit level. The set value I limit* is comparedwith the input current full wave rectified signal by the currentcontroller integration reset circuit 51a. In the control device thusarranged, the current limit level I limit* varies following the inputcurrent peak value instruction signal I PEAK*. Therefore, when the inputcurrent peak value instruction signal I PEAK* is small, the timing toreset to 0 the integrating elements of the R- and T-phase currentcontrollers 18a and 19a by an output signal of the current controllerintegration reset circuit 51a may be set at an early point. Therefore,the R- and T-phase control signals SR* and ST* are more quickly returnedto a level which makes the AC input currents flow as instructed, to morecertainly suppress the occurrence of a spike current of the inputcurrent detecting signal.

In FIG. 17, graphical description is given about the R-phase AC inputcurrent. The description is correspondingly applied to the control ofthe T-phase AC input current. The S-phase control signal SS* is formedin a manner that the subtractor 20 subtracts the R- and T-phase controlsignals SR* and ST* are subtracted from 0. Therefore, the control of theS-phase AC input current can be handled in a similar manner.

In the above-mentioned embodiment, the integrating elements are reset tozero when the AC input current exceeds its limit value. Alternatively,when the AC input current exceeds its limit value, the absolute value ofthe integrating element may be abruptly reduced.

Embodiment 7

A further embodiment of the present invention is shown in FIG. 18. Inthe embodiment, a current limit offset setter 52 and a currentcontroller integration reset circuit 51b are combined as shown. Thecurrent controller integration reset circuit 51b adds together an outputsignal I ost* of the current limit offset setter 52 and a full-waverectified signal i P* resulting from the full wave rectifying operationof the R- and T-phase input current instruction signals iR and iT , andoutputs a current limit level set value I limit*. The set value iscompared with the input current full-wave rectified signal. Theremaining circuit arrangement of the control device is the same as thatof the embodiment of FIG. 13.

FIG. 19 is a diagram showing a detailed arrangement of the currentcontroller integration reset circuit 51b in the embodiment 7 shown inFIG. 18. In the figure, reference numerals 260 and 261 designate inputterminals for receiving R- and T-phase input current detecting signalsiR and iT derived from the current detectors 14 and 15; 262, asubtractor for subtracting the R- and T-phase input current detectingsignals iR and iT coming in through the input terminals 260 and 261 fromzero and outputting the result of the subtraction in the form of anS-phase input current detecting signal iS; and 263, a full-waverectifier for full-wave rectifying the R-, S- and T-phase input currentdetecting signals iR*, iS* and iT* and outputting the result. Numerals264 and 265 indicate input terminals for receiving the R- and T-phaseinput current instruction signals iR* and iT* output from themultipliers 12 and 13; 266, a subtractor for subtracting the R- andT-phase input current instruction signals iR and iT from zero andoutputs the result in the form of an S-phase input current instructionsignal iS* and 267, a full wave rectifier for rectifying the R-, S- andT-phase input current instruction signals iR*, iS* and iT* andoutputting the result. Numeral 268, an input terminal for receiving acurrent limit offset set value I ost* that is set by and output from thecurrent limit offset setter 52; and 269, an adder for adding togetherthe full-wave rectified signal i P* of the input current command signalas the output signal of the full wave rectifier 267 and the currentlimit offset set value I ost* coming in through the input terminal 268,and outputting a current limit level set value I limit*. Numeral 270represents a comparator for comparing an input current full-waverectified signal as an output signal of the full-wave rectifier 263,viz., a maximum signal i P of the absolute values of the R-, S- andT-phase input current detecting signals iR, iS and iT, with the currentlimit level set value I limit* as an output signal of the adder 269;271, a reset signal generator for outputting a signal for resetting tozero the integrating elements of the R- and T-phase current controllers18a and 19a when the input current full-wave rectified signal i Pbecomes larger than the current limit level set value I limit*; and 272,an output terminal for outputting a reset signal generated by the resetsignal generator 271. In the thus constructed current controllerintegration reset circuit, the current limit level set value I limit* isoptimally set in accordance with the input current instruction signal.

When the input current command signal is small, the current limit levelset value I limit is also small. The timing to reset to 0 theintegrating elements of the R- and T-phase current controllers 18a and19a may be set at an early point, and it is possible to suppress theoccurrence of a spike current of the input current detecting signal.

As described above, in the control device for a PWM controlled converteraccording to the embodiment, when an AC input current exceeds a limitvalue, the absolute value of the integrating element of the currentcontrol means is abruptly reduced or reset to 0. Further, the limitvalue is set in connection with a current reference signal or a currentcommand signal output from the voltage control means. With such aconstruction, when an instantaneous power interruption, for example,takes place and the voltage of an AC power source drops or isinterrupted for a short time, no overcurrent problem arises when thepower source returns to its normal state. Accordingly, the AC inputcurrent or currents can be satisfactorily controlled. Particularly whenthe AC input current instruction signal is small, the suppression of theoccurrence of a spike current of the input current detecting signal isfurther enhanced.

Embodiment 8

In the embodiments shown in FIGS. 13, 16 and 18, when an AC inputcurrent exceeds a limit value, the absolute value of the integratingelement of the current control means is abruptly reduced or reset to 0.Instead of this, a combination of a current limit level setter 50, anintegration value comparing level setter 54, and a current controllerintegration reset circuit 51c may be used, as shown in FIG. 20. In thecontrol device using the combination, the absolute values of theintegrating elements are abruptly reduced or reset only when an AC inputcurrent exceeds a limit value, and when the integrating elements of thecurrent controllers are different in polarity from the AC referencesignals whose phases correspond to those of the integrating elements andthe electrical quantities of the input currents accumulated in theintegrating elements are in excess of a predetermined value.

In FIG. 20, like or equivalent portions are designated by like referencesymbols in FIGS. 13, 16, and 18.

FIG. 21 is a diagram showing a detailed arrangement of the currentcontroller integration reset circuit 51c. In the figure, referencenumerals 300 and 301 designate input terminals for receiving R- andT-phase input current detecting signals iR and iT from the currentdetectors 14 and 15; 302, a subtractor for subtracting the R- andT-phase input current detecting signals iR and iT coming in through theinput terminals 300 and 301 from zero and producing the result in theform of an S-phase input current detecting signal iS; and 303, afull-wave rectifier for rectifying those detecting signals iR, iS and iTand outputting the result of the rectification.

Numerals 304 and 305 represent input terminals R- and T-phase unit sinewave signals θR* and θT* synchronized with the R- and T-phase voltagesoutput from the unit sine wave generator 11; 306 and 307, comparatorsfor comparing the R-phase unit sine wave signal θR* with zero (0) andT-phase unit sine wave signal θT* with 0, and each producing "-1" whenthe input signal is positive and "+1" when it is negative; 308 and 309,input terminals for receiving the integration value signals SR-i* andST-i* as the values of the R- and T-phase integrating elements outputfrom the R- and T-phase current controllers 18c and 19c; 310 and 311,multipliers for multiplying the output signals of the comparators 306and 307 by the integration value signals SR- i* and ST-i* as the valuesof the R- and T-phase integrating elements, respectively; 312, a maximumvalue circuit for receiving the signals output from the comparators 306and 307 and outputting one signal that is the larger of the two signals;314, an input terminal for receiving an integration value comparinglevel signal Vcomp* output from the integration value comparing levelsetter 54; and 313, a comparator for comparing the integration valuecomparing level signal coming in through the input terminal 314 with theoutput signal of the maximum value circuit 312, and outputting "+1" whenthe latter is larger than the former.

Reference numeral 315 indicates an input terminal for receiving acurrent limit level set value I limit* output from the current limitlevel setter 50; 316, a comparator for comparing an input currentfull-wave rectified signal i P as the output signal of the integrator 30with a current limit level set value I limit* coming in through theinput terminal 315 and producing "+1" when i P>I limit*; 317, an ANDcircuit for producing "1" when the output signals of the comparators 316and 313 are both "1"; and 318, an integration reset signal generator forproducing through an output terminal 319 a signal for resetting theintegrating elements of the R- and T-phase current controllers 18c and19c to zero (0) when an output signal received from the AND circuit 317is "1".

The current controller integration reset circuit 51c thus constructed asshown in FIG. 21 discriminates a spike current caused in a state thatthe power source voltage is settled down into a steady state, forexample, a current overshoot caused when an R-phase input currentinstruction signal iR* is abruptly increased. Using the currentcontroller integration reset circuit thus constructed, the controldevice is operated only when the spike current can be suppressed.

When the R-phase input current instruction signal iR* is stepped orgreatly changed as shown in FIG. 22, an actual input current sometimesovershoots although it depends on the selection of a control gain of thecurrent control system. If it overshoots, the integrating term of the R-and T-phase current controllers 18c and 19c have stored signals whosephases are substantially equal to that of the power source voltage. Inthis state, if the absolute value of the integrating element isabsolutely reduced or reset, the spike current is further increased. Tocope with this, the current controller integration reset circuit 51c isdesigned so as to operate in the following manner. The comparators 306and 307 comparatively process the R- and T-phase unit sine wave signalsθR* and θT* that are synchronized in phase with the power source voltageand produce these signals in the form of signals of the invertedpolarities. The multipliers 310 and 311, respectively, multiply thosesignals and the R- and T-phase integration value signals SR-i* and ST-i*as other input signals, to thereby produce signals whose polarities arepositive when the unit sine wave signals of the respective phases areopposite in polarity to the integration value signal. Further, themaximum value circuit 312 receives those signals of the invertedpolarity and works out a maximum value of them, and the comparator 313compares the maximum value signal with the integration value comparinglevel signal Vcomp* output from the integration value comparing levelsetter 54. Only when the maximum value from the maximum value circuit islarger than the integration value comparing level signal, the outputsignal of the comparator 316 is valid.

As described above, the control device for a PWM controlled converterincludes the current control means operating such that the absolutevalues of the integrating elements are abruptly reduced or reset onlywhen an AC input current exceeds a limit value, and when the integratingelements of the current controllers are different in polarity from theAC reference signals whose phases correspond to those of the integratingelements. With such a unique construction, when an instantaneous powerinterruption, for example, takes place and the voltage of an AC powersource drops or is interrupted for a short time, no overcurrent problemarises when the power source returns to its normal state. Accordingly,the AC input current or currents can be satisfactorily controlled.Particularly when the AC input current instruction signal is stepwise orgreatly changed and the input current overshoots, the operation ofabruptly reducing or resetting the absolute values of the integratingelements are inhibited. Therefore, the occurrence of the current spikecan be more certainly suppressed independently of the set values of thecontrol gain of the current control system.

In the embodiments 5 to 8 described above, the integrating elements ofthe current control means are controlled for the AC input current. Inthe embodiments of the invention to be described hereafter, a controldevice for a PWM controlled converter will be discussed which cansatisfactorily control the AC input current also in such a state thatthe overcurrent protection trip will more easily happen, for example,when the voltage of the AC power source drops or the power supply isinterrupted for a short time in a state that large input currentinstruction signals are produced, for example, large power is suppliedto the load unit 5.

Embodiment 9

FIG. 23 is a diagram showing an arrangement of an embodiment 9 of acontrol device for a PWM controlled converter according to the presentinvention. In the figure, like or equivalent portions are designated bylike reference numerals in the above-mentioned embodiments. A voltagecontroller reset circuit 55 as one of the constituent elements of thepresent embodiment has a construction similar to that of the currentcontroller integration reset circuit 51a shown in FIG. 14. When theinput current of R-, S- or T-phase is larger than the current limitlevel set value I limit*, the voltage controller reset circuit 55operates to reset the integrating element of a voltage controller 9b tozero. Where it is reset, the R- and-T-phase input current instructionsignals iR* and iT* are also zero. As a result, the restoring of theintegrating elements of the current controllers to their original statesis quickened, so that an occurrence of the current spike is suppressed.

FIG. 24 is a diagram useful in explaining an operation of the embodimentshown in FIG. 23. In the figure, only the waveforms of the voltages andcurrents of R-phase are typically illustrated for ease of explanation.In the figure, in a duration (A) where the power source is interruptedand another duration (B) where the R-phase input current detectingsignal iR is below the R-phase input current instruction signal iR*, theR-phase control signal SR* is progressively accumulated in theincreasing direction of the R-phase input current detecting signal iR.Its accumulation stops at a point in time (C) where the R-phase inputcurrent detecting signal iR is equal to the R-phase input currentinstruction signal iR*. Thereafter, at a point in time (D) where itexceeds the set value I limit* of the current limit level, theintegrating element of the voltage controller 9b is reset to zero (0),and the R-phase input-current instruction signal iR also becomes zero.The input signal to the current controller sharply increases, and thereturning of the control device to a normal operating state isquickened.

As seen from the foregoing description, the control device for a PWMcontrolled converter includes the voltage control means operating suchthat when the AC input current exceeds its limit value, the voltagecontrol means abruptly reduces or resets the integrating element of thevoltage controller. With such a unique construction, when aninstantaneous power interruption, for example, takes place and thevoltage of an AC power source drops or is interrupted for a short time,no overcurrent problem arises when the power source returns to itsnormal state. Therefore, a satisfactory control of the AC input currentor currents is secured. Particularly when the AC input currentinstruction value is large, viz., the input current peak valueinstruction signal I PEAK* is large, a more effective suppression of thespike current occurrence is ensured.

Embodiment 10

In the embodiment 9, when the input current of R-, S- or T-phase islarger than the current limit level set value I limit*, the voltagecontroller reset circuit 55 operates to reset the integrating element ofa voltage controller 9b to zero. As shown in FIG. 25, an input currentpeak value instruction signal selector 56 may be used.

In FIG. 25, like or equivalent portions are designated by like referencesymbols in FIG. 23.

FIG. 26 is a diagram showing a detailed arrangement of the input currentpeak value instruction signal selector 56. In the figure, referencenumerals 400 and 401 designate input terminals for receiving R- andT-phase input current detecting signals iR and iT from the currentdetectors 14 and 15; 402, a subtractor for subtracting from zero the R-and T-phase input current detecting signals iR and iT coming in throughthe input terminals 400 and 401 and outputting the result in the form ofan S-phase input current detecting signal iS; 403, a full-wave rectifierfor rectifying the R-, S- and T-phase input current detecting signalsand outputting the rectified ones; and 404, an input terminal forreceiving a current limit level set value I limit* output from thecurrent limit level setter 50. Numeral 405 designates a comparator forcomparing a full-wave rectified signal as an output signal of thefull-wave rectifier 403, viz., a maximum signal i P of the absolutevalues of the R-, S- and T-phase input currents with the set value Ilimit* of the current limit level coming through the input terminal 254;406, an input terminal for receiving a peak value instruction signal IPEAK* of the input current as an output signal of the voltage controller9d; 407 and 408, switches for selecting a signal; 409, a first order lagcircuit for outputting an input signal in the form of a time function;and 410, an output terminal for outputting the input current peak valueinstruction signal I PEAK* coming in through the input terminal 406 oran output signal of the first order lag circuit 409 to the multipliers12 and 13.

An operation of the input current peak value instruction signal selector56 will be described hereunder. When the input current full-waverectified signal i P as an output signal of the full-wave rectifier 403is smaller than the current limit level set value I limit* coming inthrough the input terminal 404, the switches 407 and 408 are turned topositions (B). In this state, the input current peak value instructionsignal I PEAK* as an output signal of the voltage controller 9d, whichcomes in through the input terminal 406, is straightforwardly outputthrough the output terminal 410. When the input current full-waverectified signal i P as an output signal of the full-wave rectifier 403is larger than the current limit level set value I limit* coming inthrough the input terminal 404, the switches 407 and 408 are turned topositions (A). In this state, the input current peak value instructionsignal I PEAK* as an output signal of the voltage controller 9d, whichcomes in through the input terminal 406, is input to the first order lagcircuit 409. In the first order lag circuit, it is transformed into asignal that increases from zero with time, and eventually reaches thepeak value instruction signal I PEAK* of the original input current.This signal is output through the output terminal 410.

As described above, in the embodiment, the control device for a PWMcontrolled converter includes the voltage control means operating suchthat when an AC input current exceeds its limit value, the voltagecontrol means varies a current reference signal as defined by a timefunction of which an initial value is the current reference signalsmaller than the current reference signal at least at the time pointwhere the input current exceeds the limit value. Therefore, when adeviation eV of a DC voltage detecting value V DC detected by thevoltage detector 7 from a voltage instruction value V DC* output fromthe voltage setter 6 is large, viz., an input current peak valueinstruction signal I PEAK* is caused by the proportional element of thevoltage controller 9d, the R- and T-phase input current instructionsignals iR* and iT* can be reduced to zero. Accordingly, the inputcurrents to the current controllers sharply increase to thereby quickenthe returning of the control device to its normal state.

Embodiment 11

In the embodiments 9 and 10, a current limit level set value I limit* isset in advance by the current limit level setter 50. An embodiment shownin FIG. 27 uses a combination of a current limit level setter 50, anintegration value comparing level setter 54, and a voltage controllerintegration reset circuit 57. With the use of the combination, anabsolute value of the integrating element of the voltage controller 9bis abruptly reduced or reset when an AC input current exceeds a limitvalue, and when the integrating elements are different in polarity fromthe AC reference signals whose phases correspond to those of theintegrating elements and the electrical quantities of the input currentsaccumulated in the integrating elements are in excess of a predeterminedvalue.

In FIG. 27, like or equivalent portions are designated by like referencesymbols in the embodiments 8 and 10. The detailed construction of thevoltage controller integration reset circuit 57 is the same as of thecurrent controller integration reset circuit 51c. Hence, no furtherdescription of it will be given.

As described above, the control device for a PWM controlled converter ofthe present embodiment includes current control means operating suchthat an absolute value of the integrating element of the voltagecontroller is abruptly reduced or reset when an AC input current exceedsits limit value, and when the integrating elements of the currentcontrol means are different in polarity from the AC reference signals.With such a unique construction, when an instantaneous powerinterruption, for example, takes place and the voltage of an AC powersource drops or is interrupted for a short time, no overcurrent problemarises when the power source returns to its normal state. Therefore, asatisfactory control of the AC input current or currents is secured.Particularly when the AC input current instruction value is large, viz.,the input current peak value instruction signal is large, a moreeffective suppression of the spike current occurrence is ensured.Further, when the AC input current instruction signal is stepwise orgreatly changed and the input current overshoots, the operation ofabruptly reducing or resetting the absolute value of the integratingelement are inhibited. Therefore, the occurrence of the current spikecan be more certainly suppressed independently of the set values of thecontrol gain of the current control system.

Suitable combinations of the above-mentioned embodiments can provide afurther effective suppression of the current spike occurrence, as amatter of course. The reactors inserted between the 3-phase AC powersource and the PWM controlled converter are not essential and may besubstituted by reactance components of the transformer, for example, ofthe 3-phase AC power source 1.

As described above, there is provided a control device for a PWMcontrolled converter having voltage control means for comparing with avoltage set value a detecting value of a DC voltage output from the PWMcontrolled converter, connected through reactors to a 3-phase AC powersource, for controlling AC input currents supplied from the 3-phase ACpower source, to thereby produce current reference signals, AC referencesignal generating means for generating AC reference signals synchronizedwith the 3-phase AC power source, current instruction means forproducing current instruction signals formed by varying the amplitudesof the AC reference signals output from the AC reference signalgenerating means in accordance with the current reference signals, andcurrent control means for producing control signals to the PWMcontrolled converter so that the AC input currents vary as instructed bythe current instruction signals, the improvement characterized in thatthe current control means produces control signals based on aproportional control for a predetermined period after the controlstarts, and produces other control signals based on a proportionalintegration control after the predetermined period is terminated. In aspecific case, at starting the proportional control basis controlsignals are used for controlling the PWM controlled converter for apredetermined period, and after the predetermined period terminates, theproportional-integration-control basis control signals are used forcontrolling the PWM controlled converter. Therefore, no overcurrentproblem arises, and a good control of the input currents is secured.

In the control device for a PWM controlled converter according to thefirst embodiment, the current control means produces the control signalsbased on the proportional integration control at the instant that adetecting value of the DC voltage output from the PWM controlledconverter exceeds a predetermined value. Therefore, a proportionalcontrol mode is switched to a proportional integration control mode andvice versa at an optimum switching timing. Particularly at starting, agood input current control can be carried out without causing theovercurrent problem, for example. Additionally, the proportional controlperiod possibly causing a steady deviation may easily be minimized inconsideration of the overall circuit arrangement.

The present invention also provides a control device for a PWMcontrolled converter having voltage control means for comparing with avoltage set value a detecting value of a DC voltage output from the PWMcontrolled converter, connected through reactors to a 3-phase AC powersource, for controlling AC input currents supplied from the 3-phase ACpower source, to thereby produce current reference signals, AC referencesignal generating means for generating AC reference signals synchronizedwith the 3-phase AC power source, current instruction means forproducing current instruction signals formed by varying the amplitudesof the AC reference signals output from the AC reference signalgenerating means in accordance with the current reference signals, andcurrent control means for producing control signals to the PWMcontrolled converter so that the AC input currents vary as instructed bythe current instruction signals, the improvement characterized in thatthe current control means multiplies the deviations of AC input currentsfrom the current instruction signals of two of three phases output fromthe current instruction means by first coefficients, integrates theresults of the multiplications, and outputs the results of theintegrations in the form of first output signals of the two phases, addstogether the sign inverse values of the first output signals of the twophases to form a first output signal of the remaining phase, multipliesthe deviations of the AC input currents from the input currentinstruction signals by second coefficients to form second output signalsof the respective phases, adds together the first and second outputsignals for each phase and outputs the sums in the form of controlsignals applied to the PWM controlled converter. Thus, the proportionalcontrol is performed on at least one phase. Therefore, at starting noovercurrent problem arises. Even when the DC side voltage V DC drops bya load variation, no overcurrent problem arises, and good currentcontrol is secured.

The invention further provides a control device for a PWM controlledconverter having DC voltage detecting means for detecting a DC voltageoutput from the PWM controlled converter for controlling AC inputcurrents supplied from a 3-phase AC power source, voltage instructionoutputting means for outputting an instruction value of the DC voltage,voltage control means for comparing a voltage instruction value outputfrom the voltage instruction outputting means with a voltage detectingvalue output from the DC voltage detecting means, to thereby producecurrent reference signals, and current control means for producingcontrol signals to the PWM controlled converter so that the AC inputcurrents vary as instructed by the current instruction signals obtainedfrom the current reference signals, the improvement characterized inthat the voltage instruction outputting means calculatingly corrects thedetection errors to produce a voltage instruction value. Therefore,there is eliminated the use of a variable resistor, for example, forcompensating for the offset or gain error of the voltage detectingcircuit. Hence, troublesome compensating work is eliminated and theoperability of the control device is improved. Further, the work foradjusting the offset and gain errors can efficiently be done in thestage of manufacturing.

In the control device for a PWM controlled converter the voltageinstruction outputting means includes storing means for storing therelationships between the values of the known voltages applied to the DCvoltage detecting means and the detecting voltage values, detected bythe DC voltage detecting means, corresponding to the known voltages, andcorrecting means for calculatingly correcting a voltage instructionvalue by using the stored voltage relationships so that an actual DCvoltage output from the PWM controlled converter is settled down at adesired value. Therefore, there is eliminated the use of a variableresistor, for example, for compensating for the offset or gain error ofthe voltage detecting circuit. Hence, the operability of the controldevice is improved. Further, the operation for adjusting the offset andgain errors can easily be automated in the stage of manufacturing.

In the control device for a PWM controlled converter, the known voltagesapplied to the DC voltage detecting means are DC voltages output fromthe PWM controlled converter. Therefore, the calculation for correctinga voltage instruction value using the known voltages can be realized bya simple circuit, not using a specially designed circuit.

In the control device for a PWM controlled converter, the voltageinstruction outputting means includes storing means for storing therelationships between the voltages output from a reference voltagegenerating means included in the DC voltage detecting means and thedetecting voltage values, detected by the DC voltage detecting means,corresponding to the voltages output from the reference voltagegenerating means, and correcting means for calculatingly correcting avoltage instruction value by using the stored voltage relationships sothat an actual DC voltage output from the PWM controlled converter issettled down at a desired value. Therefore, the calculation forcorrecting a voltage instruction value using the known voltages can berealized by a simple circuit, not using a DC power source of a highvoltage comparable with the DC side voltage V DC in a normal operatingstate.

The invention also provides a control device for a PWM controlledconverter having voltage control means for comparing a voltage set valuewith a detecting value of a DC voltage output from the PWM controlledconverter, connected to an AC power source, for controlling AC inputcurrents supplied form the AC power source, to thereby produce a currentreference signal, AC reference signal outputting means for outputting ACreference signals synchronized with the AC power source, currentinstruction means for producing current instruction signals formed byvarying the amplitudes of the AC reference signals output from the ACreference signal outputting means in accordance with the currentreference signal, and current control means, including at leastintegrating elements, for producing control signals to the PWMcontrolled converter so that the AC input currents vary as instructed bythe current instruction signals, the improvement characterized in thatwhen an AC input current exceeds a predetermined limit value, thecurrent control means abruptly reduces the integrating elements thereof.With such a unique construction, when an instantaneous powerinterruption, for example, takes place and the voltage of an AC powersource drops or is interrupted for a short time, no overcurrent problemarises when the power source returns to its normal state. Accordingly,the AC input current or currents can be satisfactorily controlled.

In the control device for a PWM controlled converter, when an AC inputcurrent exceeds a predetermined limit value, the current control meansresets the integrating elements thereof to zero (0). Therefore, when aninstantaneous power interruption, for example, takes place and thevoltage of an AC power source drops or is interrupted for a short time,no overcurrent problem arises when the power source returns to itsnormal state. Accordingly, the AC input current or currents can bereliably controlled.

In the control device, the limit value is set on the basis of thecurrent reference signal output from the voltage control means.Therefore, when an instantaneous power interruption, for example, takesplace and the voltage of an AC power source drops or is interrupted fora short time, no overcurrent problem arises when the power sourcereturns to its normal state. Accordingly, a good control of AC inputcurrent or currents is secured. Particularly when the instruction valueof the AC input current is small, a current spike in the input currentdetecting signal is more certainly suppressed in its occurrence.

In the control device, the limit value is set on the basis of thecurrent instruction signals output from the current instruction means.Accordingly, the limit value varies in accordance with the input currentpeak value instruction signal I PEAK*. Therefore, particularly when thepeak value instruction signal I PEAK* is small, the timing to reset to 0the integrating elements of the current controllers may be set at anearly point. Therefore, the control signals are more quickly returned tosuch a level as to make the AC input currents flow as instructed to morecertainly suppress the occurrence of a spike current of the inputcurrent detecting signal.

In the control device, the current control means includes a currentlimit Level setter for setting a limit value of an AC input current anda current controller integration reset circuit connected for receptionto the limit value set by the current limit level setter and AC inputcurrents, when the AC input current exceeds the limit value, the currentcontroller integration reset circuit produces a signal. Therefore, whenan instantaneous power interruption, for example, takes place and thevoltage of an AC power source drops or is interrupted for a short time,the AC input current can be controlled free from the overcurrent problemwhich otherwise arises when the power source returns to its normalstate.

In the control device, the current control means abruptly reduces theabsolute values of the integrating elements when an AC input currentexceeds a limit value, and when the integrating elements of the currentcontrol means are different in polarity from the AC reference signalswhose phases correspond to those of the integrating elements and theelectrical quantities of the input currents accumulated in theintegrating elements are in excess of a predetermined value. With such aunique construction, when an instantaneous power interruption, forexample, takes place and the voltage of an AC power source drops or isinterrupted for a short time, no overcurrent problem arises when thepower source returns to its normal state. Accordingly, the AC inputcurrent or currents can be satisfactorily controlled. Particularly whenthe AC input current instruction signal is stepwise or greatly changedand the input current overshoots, the operation of abruptly reducing orresetting the absolute values of the integrating elements is inhibited.Therefore, the occurrence of the current spike can be more certainlysuppressed independently of the set values of the control gain of thecurrent control system.

The invention additionally provides a control device for a PWMcontrolled converter having voltage control means for comparing avoltage set value with a detecting value of DC voltage output from thePWM controlled converter, connected to an AC power source, forcontrolling AC input currents supplied form the AC power source, tothereby produce a current reference signal, AC reference signaloutputting means for outputting AC reference signals synchronized withthe AC power source, current instruction means for producing currentinstruction signals formed by varying the amplitudes of the AC referencesignals output from the AC reference signal outputting means inaccordance with the current reference signal, and current control meansfor producing control signals to the PWM controlled converter so thatthe AC input currents vary as instructed by the current instructionsignals, the improvement characterized in that when an AC input currentexceeds a predetermined limit value, the current control means abruptlyreduces the current reference signals. With such a unique construction,when an instantaneous power interruption, for example, takes place andthe voltage of an AC power source drops or is interrupted for a shorttime, no overcurrent problem arises when the power source returns to itsnormal state. Therefore, a satisfactory control of the AC input currentor currents is secured. Particularly when the AC input currentinstruction value is large, viz., the input current peak valueinstruction signal I PEAK* is large, a more effective suppression of thespike current occurrence is ensured.

In the control device, the current control means includes integratingelements, and when an AC input current exceeds a predetermined limitvalue, resets the integrating elements to zero (0). With such a uniqueconstruction, when an instantaneous power interruption, for example,takes place and the voltage of an AC power source drops or isinterrupted for a short time, no overcurrent problem arises when thepower source returns to its normal state, and hence the AC input currentcan reliably be controlled.

In the control device, when an AC input current exceeds a predeterminedlimit value, the voltage control means varies a current reference signalas defined by a time function of which an initial value is the currentreference signal smaller than the current reference signal at least atthe time when the input current exceeds the limit value. Accordingly,the input currents to the current controllers sharply increase tothereby quickly return the control device to its normal state.

In the control device, when an AC input current exceeds a predeterminedlimit value, and when the integrating elements of the current controlmeans are different in polarity from the AC reference signals whosephases correspond to those of the integrating elements and theelectrical quantities of the input currents accumulated in theintegrating elements are in excess of a predetermined value, the currentcontrol means reduces the current reference signal. With such a uniqueconstruction, when an instantaneous power interruption, for example,takes place and the voltage of an AC power source drops or isinterrupted for a short time, no overcurrent problem arises when thepower source returns to its normal state. Therefore, a satisfactorycontrol of the AC input current or currents is secured. Particularly,when the AC input current instruction value is large, viz., the inputcurrent peak value instruction signal is large, a more effectivesuppression of the spike current occurrence is ensured. Further, whenthe AC input current instruction signal is stepwise or greatly changedand the input current overshoots, the operation of abruptly reducing orresetting the absolute value of the integrating element is inhibited.Therefore, the occurrence of the current spike can be more certainlysuppressed independently of the set values of the control gain of thecurrent control system.

What is claimed is:
 1. A control device for a PWM controlled converterhaving voltage control means for comparing with a voltage set value adetection value of a DC voltage output from said PWM controlledconverter, connected through reactors to a 3-phase AC power source, forcontrolling AC input currents supplied from said 3-phase AC powersource, to thereby produce current reference signals, AC referencesignal generating means for generating AC reference signals synchronizedwith said 3-phase AC power source, current instruction means forproducing current instruction signals formed by varying the amplitudesof said AC reference signals output from said AC reference signalgenerating means in accordance with said current reference signals, andcurrent control means for producing control signals to said PWMcontrolled converter so that said AC input currents vary as instructedby said current instruction signals, the improvement characterized inthat said current control means produces control signals based on aproportional control for a predetermined period after the controlstarts, and produces other control signals based on a proportionalintegration control after said predetermined period is terminated. 2.The control device for a PWM controlled converter according to claim 1,in which said current control means produces the control signals basedon the proportional integration control when the detected value of theDC voltage output from said PWM controlled converter exceeds apredetermined value.
 3. A control device for a PWM controlled converterhaving voltage control means for comparing with a voltage set value adetection value of a DC voltage output from said PWM controlledconverter, connected through reactors to a 3-phase AC power source, forcontrolling AC input currents supplied from said 3-phase AC powersource, to thereby produce current reference signals, AC referencesignal generating means for generating AC reference signals synchronizedwith said 3-phase AC power source, current instruction means forproducing current instruction signals formed by varying the amplitudesof said AC reference signals output from said AC reference signalgenerating means in accordance with said current reference signals, andcurrent control means for producing control signals to said PWMcontrolled converter so that said AC input currents vary as instructedby said current instruction signals, the improvement characterized inthat said current control means multiplies the deviations of AC inputcurrents from the current instruction signals of two of three phasesoutput from said current instruction means by first coefficients,integrates the results of the multiplications, and outputs the resultsof the integrations in the form of first output signals of the twophases, adds together the sign inverse values of said first outputsignals of the two phases to form a first output signal of the remainingphase, multiplies the deviations of the AC input currents from the inputcurrent instruction signals by second coefficients to form second outputsignals of the respective phases, adds together said first and secondoutput signals for each phase and outputs the sums in the form ofcontrol signals applied to the PWM controlled converter.
 4. A controldevice for a PWM controlled converter having DC voltage detecting meansfor detecting a DC voltage output from said PWM controlled converter forcontrolling AC input currents supplied from a 3-phase AC power source,voltage instruction outputting means for outputting a voltageinstruction value of the DC voltage, voltage control means for comparingthe voltage instruction value output from said voltage instructionoutputting means with a voltage detection value output from said DCvoltage detecting means, to thereby produce current reference signals,and current control means for producing control signals to said PWMcontrolled converter so that said AC input currents vary as instructedby said current instruction signals obtained from said current referencesignals, the improvement characterized in that said voltage instructionoutputting means performs calculations to correct detection errors ofthe voltage detection value to produce the voltage instruction value. 5.The control device for a PWM controlled converter according to claim 4,in which said voltage instruction outputting means includes storingmeans for storing relationships between values of known voltages appliedto said DC voltage detecting means and values of the detected DC voltageoutput from said PWM controlled converter and detected by said DCvoltage detecting means, corresponding to said known voltages, andcorrecting means for performing calculations to correct a voltageinstruction value by using the stored voltage relationships so that anactual DC voltage output from said PWM controlled converter achieves andmaintains a desired value.
 6. The control device for a PWM controlledconverter according to claim 5, in which said known voltages applied tosaid DC voltage detecting means are DC voltages output from said PWMcontrolled converter.
 7. The control device for a PWM controlledconverter according to claim 4, in which said voltage instructionoutputting means includes storing means for storing relationshipsbetween voltages output from a reference voltage generating meansincluded in said DC voltage detecting means and detected voltage values,detected by said DC voltage detecting means, corresponding to thevoltages output from said reference voltage generating means, andcorrecting means for performing calculation to correct a voltageinstruction value by using the stored voltage relationships so that anactual DC voltage output from said PWM controlled converter achieves andmaintains a desired value.
 8. A control device for a PWM controlledconverter having voltage control means for comparing a voltage set valuewith a detecting value of a DC voltage output from said PWM controlledconverter, connected to an AC power source, for controlling AC inputcurrents supplied from said AC power source, to thereby produce acurrent reference signal, AC reference signal outputting means foroutputting AC reference signals synchronized with said AC power source,current instruction means for producing current instruction signalsformed by varying the amplitudes of said AC reference signals outputfrom said AC reference signal outputting means in accordance with saidcurrent reference signal, and current control means, including at leastintegrating elements, for producing control signals to said PWMcontrolled converter so that said AC input currents vary as instructedby said current instruction signals, the improvement characterized inthat when at least one of said AC input currents exceeds a limit value,said current control means abruptly reduces a value of the integratingelements thereof.
 9. The control device for a PWM controlled converteraccording to claim 8, in which when at least one of said AC inputcurrents exceeds the limit value, said current control means resets theintegrating elements thereof to zero (0).
 10. The control device for aPWM controlled converter according to claim 8, in which said limit valueis set on the basis of said current reference signal output from saidvoltage control means.
 11. The control device for a PWM controlledconverter according to claim 8, in which said limit value is set on thebasis of the current instruction signals output from said currentinstruction means.
 12. The control device for a PWM controlled converteraccording to claim 8, in which said current control means includes acurrent limit level setter for setting the limit value of an AC inputcurrent and a current controller integration reset circuit connected toreceive the limit value set by said current limit level setter and ACinput currents, and when at least one of said AC input currents exceedssaid limit value, said current controller integration reset circuitproduces a signal.
 13. The control device for a PWM controlled converteraccording to claim 8, in which said current control means abruptlyreduces the absolute values of the integrating elements when at leastone of said AC input currents exceeds the limit value, and when theintegrating elements of said current control means are different inpolarity from the AC reference signals whose phases correspond to thoseof the integrating elements and the electrical quantities of the inputcurrents accumulated in the integrating elements are in excess of apredetermined value.
 14. A control device for a PWM controlled converterhaving voltage control means for comparing a voltage set value with adetection value of a DC voltage output from said PWM controlledconverter, connected to an AC power source, for controlling AC inputcurrents supplied from said AC power source, to thereby produce acurrent reference signal, AC reference signal outputting means foroutputting AC reference signals synchronized with said AC power source,current instruction means for producing current instruction signalsformed by varying the amplitudes of said AC reference signals outputfrom said AC reference signal outputting means in accordance with saidcurrent reference signal, and current control means for producingcontrol signals to said PWM controlled converter so that said AC inputcurrents vary as instructed by said current instruction signals, theimprovement characterized in that when at least one of said AC inputcurrents exceeds a limit value, said current control means abruptlyreduces said current reference signal.
 15. The control device for a PWMcontrolled converter according to claim 14, in which said currentcontrol means includes integrating elements, and when at least one ofsaid AC input currents exceeds the limit value, resets said integratingelements to zero (0).
 16. The control device for a PWM controlledconverter according to claim 14, in which when at least one of said ACinput currents exceeds the limit value, said voltage control meansvaries a current reference signal as defined by a time function of whichan initial value is the current reference signal and has a value smallerthan the current reference signal when the input current exceeds thelimit value.
 17. The control device for a PWM controlled converteraccording to claim 14, in which when at least one of said AC inputcurrents exceeds the limit value, and when the integrating elements ofsaid current control means are different in polarity from the ACreference signals whose phases correspond to those of the integratingelements and the electrical quantities of the input currents accumulatedin the integrating elements are in excess of a predetermined value, saidcurrent control means reduces the current reference signal.